ASTRONOMY 


ASTRONOMY 


BY 

GEORGE    F.    CHAMBERS,    F.R.A.S. 

Of  the  Inner  Temple,  Barrister-at-Law 

AUTHOR   OF    "  A    HANDBOOK    OF    ASTRONOMY,"    "  THE   STORY 
OF    THE   COMETS,"    AND   OTHER   WORKS 


WITH  358  ILLUSTRATIONS,  INCLUDING  8  COLOURED  PLATES 


Gold  Medal  of.th  -  R.iya- 
A  str^nont  -V* ;/  Societv 


NEW  YORK 

D.    VAN    NOSTRAND    COMPANY 
TWENTY-FIVE    PARK   PLACE 


PRINTED    IN    GREAT   BRITAIN 


PREFACE. 

THIS  volume  is  not  a  formal  treatise  on  Astronomy,  nor  is  it 
a  mere  educational  text-book  ;  but  the  idea  which  underlies 
it  may  be  realised  from  the  following  considerations.  An 
extended  experience  as  an  astronomical  writer,  and  likewise 
lecturer  on  the  science,  coupled  with  much  intercommunica- 
tion with  many  of  its  votaries  in  divers  walks  of  life  and 
places,  including  colonies  and  foreign  countries,  has  led  me 
to  notice  the  remarkable  spread  of  late  years  all  over  the 
world  of  a  taste  for  Astronomy.  Some  recent  eclipses  of 
the  Sun,  and  especially  some  recent  comets,  have  had  a  good 
deal  to  do  with  this,  especially  Halley's  Comet  of  1910.  I 
have  often  been  struck  by  the  frequent  requests  for  informa- 
tion on  astronomical  topics  from  all  sorts  of  people,  the 
majority  of  whom,  I  fancy,  would  have  resented  a  suggestion 
that  they  should  sit  down  and  seriously  study  text-books  on 
the  subject.  These  are  the  people  whom  I  want  to  get  hold  of 
through  this  volume. 

There  is  nothing  profound  or  inconveniently  deep  in  it, 
but  it  just  gives  a  popular  outline  of  leading  facts,  which 
may  be  easily  grasped  by  any  fairly  educated  person  who  is 
only  able,  or  disposed,  to  give  a  limited  amount  of  time  or 
•thought  to  the  matter,  but  who  may  happen  to  possess  a 
small  telescope  of,  say,  two  or  three  inches  aperture,  or  even 
a  good  opera-glass.  My  endeavour  has  been  to  deal  descrip- 

285716 


VI  PREFACE, 

tively  with  some  of  the  more  ordinary  sights  of  the  Heavens, 
the  examination  of  many  of  which  can  be  carried  out  with 
the  class  of  instrument  just  mentioned.  Mathematical  and 
theoretical  matters  and  speculations  have  been  kept  entirely 
in  the  background. 

It  will  appear,  I  hope,  from  the  foregoing  statement  that 
my  idea  has  been  to  direct  the  reader's  attention  to  what 
may  be  called  every-day  topics,  and  to  give  in  a  handy  form 
information  on  such  phenomena  as  are  constantly  brought 
under  the  notice  of  people  in  general  without  exactly  being 
sought  for  by  them.  I  want  the  reader  to  be  able  to  answer 
such  questions  as,  "  What  is  the  meaning  of  the  term  Sun- 
spot?"  "What  is  the  name  of  that  bright  star,  or  is  it  a 
planet,  which  I  see  in  the  west  every  evening  ? "  "  Is  there 
any  difference  between  an  eclipse  of  the  Sun  and  an  eclipse 
of  the  Moon?"  "Was  Sir  George  Cornwall  Lewis  right 
when  he  stigmatised  Astronomy  as  a  science  of  'pure 
curiosity '?  " 

Such  questions  as  these,  and  others  much  more  shallow, 
have  often  been  addressed  to  me,  and  I  want  to  provide 
people  who  possess  only  a  smattering  of  scientific  knowledge 
with  the  means  of  answering  some  of  these  questions  which 
frequently  crop  up  when  some  noteworthy  astronomical  event 
or  discovery  gets  mentioned  in  the  newspapers  or  is  talked 
about.  It  will  be  seen,  I  think,  that  whilst  my  aims  are 
modest,  I  have  endeavoured  to  provide  materials  for  sensible 
and  exact  knowledge,  truly  scientific  and  correct,  yet  not 
needing  too  severe  a  demand  on  the  time  or  mental  powers 
of  those  who  patronise  the  book. 

The  illustrations  have  been  obtained  from  many  sources, 
and,  whilst  it  may  be  said  of  some  of  them  that  they  are  not 
new,  or  only  reproduce  old  ideas  in  new  form,  yet  I  have 
endeavoured  as  far  as  possible  to  be  chary  in  the  insertion 


PREFACE.  vil 

of  such,  being  desirous  of  providing  my  readers  with  pictures 
which  are  not  in  general  circulation  or  accessible  to  the 
reading  public.  This  really  means  that  I  have  ransacked  the 
publications  of  various  scientific  societies,  European  and 
American,  for  illustrations.  America  has  been  a  rich  field 
for  this  purpose. 

I  have  to  thank  Mr.  H.  F.  Bushell,  of  the  Gresham  School, 
Holt,  Norfolk,  for  kindly  reading  the  proof-sheets,  but  my 
special  thanks  are  due  to  friends  too  numerous  to  mention  all 
by  name,  who  have  provided  me  with  drawings  and  photo- 
graphs, without  which  it  would  have  been  impossible  to 
produce  this,  the  most  copiously  illustrated  book  on  Astro- 
nomy which,  I  should  suppose,  has  ever  been  published. 
There  are,  however,  a  few  names  which  stand  out  more 
conspicuously  than  others,  and  which  must  receive  special 
mention.  In  such  a  list  I  must  include  the  following  :  Pro- 
fessor E.  E.  Barnard,  of  the  Yerkes  Observatory,  Williams- 
town  ;  Professor  W.  H.  Pickering,  of  the  Harvard  College 
Observatory,  an  institution  to  which  Astronomy  owes  more 
than  can  be  expressed  ;  the  Councils  of  the  Royal  Astrono- 
mical Society  and  of  the  British  Astronomical  Association  ; 
and  several  private  friends,  under  which  head  there  must  be 
included  Mr.  E.  M.  Antoniadi,  Mr.  E.  H.  Barlow,  Mr.  S.  Bolton, 
Rev.  A.  L.  Cortie,  S.J.,Mr.  W.  F.  Denning,  Mr.  W.  B.  Gibbs, 
Mr.  F.  W.  Longbottom,  Admiral  Moore,  Rev.  T.  E.  R.  Phillips, 
Mr.  W.  E.  Wilson,  Mr.  H.  E.  Wood,  together  with  Messrs. 
Cooke  &  Sons  and  Sir  H.  Grubb. 


AN  attentive,  or  even  a  cursory,  perusal  of  this  book  will 
give  the  go-by  to  the  idea  that  astronomy  is  a  science  of  "  pure 
curiosity."  On  the  contrary,  it  has  a  great  deal  to  recommend 
it  even  in  this  utilitarian  age,  for  the  navigation  of  the  high 
waters  of  the  world,  and  the  daily  disposal  of  our  time  by  all  of 
us  by  the  agency  of  clocks  and  watches,  depend  upon  the 
practical  application  of  astronomy  to  the  concerns  of  daily  life. 
But  over  and  above  all  this  it  is  a  science  which  points  un- 
mistakeably  to  the  Universe  having  been  created,  and  being 
still  maintained,  by  a  Divine  Hand  which  controls  everybody 
and  everything  around  us.  It  was  no  poetical  fancy  which 
inspired  Young  in  his  Night  Thoughts  to  write  the  significant 
words  "  An  undevout  astronomer  is  mad." 

G.  F.  C. 
Lethen  Grange, 
Sydenham. 


CONTENTS. 

PREFACE    .         .  .         .  .  .  pp.  v-vii 

CONTENTS  .         . ..,       .  ...  .  .  ix-xiv 

LIST  OF  ILLUSTRATIONS  .                   .  .  .  xv-xxiii 

THE  GREEK  ALPHABET  .         ...  .  .  xxiv 

CHAPTER  I. 
INTRODUCTION. 

The  scope  of  the  Science  of  Astronomy. — Its  modern  developement — 
The  other  sciences  which  come  in  contact  with  it. — The  resulting  necessity 
of  keeping  the  treatment  of  the  science  within  defined  limits. — The  different 
divisions  of  pure  astronomy. — Mathematical  Astronomy. — Lord  Grim- 
thorpe's  book,  "  Astronomy  without  Mathematics." — Theoretical  As- 
tronomy.— Descriptive,  or  Visual  Astronomy. — Practical  Astronomy. 
— Amateurs  may  dispense  with  knowledge  of  mathematics  altogether  and 
of  the  theory  of  telescopes  and  optics  in  part. — The  modern  application  of 
the  spectroscope .  .  .  .  .  <•  .  .  pp.  1-4 

CHAPTER  II. 
THE  SUN. 

Important  position  occupied  by  the  Sun. — Its  general  appearance. — Its 
mottled  surface. — "Granulations"  probably  the  best  word  to  describe  it. 
— Spots  on  the  Sun. — Their  periodicity. — General  description  of  them. — 
Peculiarities  of  spots. — Period  of  the  Sun's  rotation. — The  Photosphere. 
— Distribution  of  the  spots  in  latitude. — Discovery  of  the  periodicity  of 
the  spots. — Aurora. — Terrestrial  magnetism. — Sun-spots  and  terrestrial 
weather. — Possible  influence  of  some  of  the  planets  on  Sun-spots. — 
Wilson's  theory  respecting  them. — Vortex  movements  on  the  Sun. — Facula. 
— Apparent  movements  of  spots  at  different  seasons  of  the  year. — Notable 
large  spots. — Light-  and-heat- giving  powers  of  the  Sun. — The  Krakatoa 
sunsets.  .........  pp.  5-25 


X  CONTENTS. 

CHAPTER  III. 
THE  MOON. 

Next  after  the  Sun  in  popular  interest. — How  soon  visible  after  being 
new. — Its  phases. — Its  movement  through  the  heavens. — General  physical 
aspects. — Its  mountains. — The  walled  plains. — The  rills. — Mountain 
chains. — Isolated  peaks. — Signs  of  volcanic  action. — Resemblance  be- 
tween lunar  and  terrestrial  volcanoes. — Names  applied  to  the  principal 
mountains. — The  so-called  seas  on  the  Moon. — General  appearance  of 
a  crater. — Changes  in  their  appearance  owing  to  the  Moon's  axial  rotation. 
— The  motions  of  the  Moon  very  complex. — The  Librations. — -The  Harvest 
Moon. — The  Hunter's  Moon. — Brightness  of  the  Moon  compared  with  the 
Sun. — Supposed  influence  of  the  Moon  on  the  weather. — Other  influences 
ascribed  to  the  Moon. — The  "  New  Moon  in  the  Old  Moon's  Arms." 
— Influence  of  the  Moon  on  clouds. — Influence  of  Moonlight  on  human 
beings,  a  fallacy. — Some  statistics  .....  pp.  26-40 

CHAPTER  IV. 

THE  TIDES. 

The  tides  matter  of  interest  to  the  inhabitants  of  maritime  countries. — 
Influence  of  the  Sun  and  Moon  in  causing  them. — Details  of  this  influence. 
— That  of  the  Moon  greatly  preponderates. — Spring  Tides. — Neap  Tides. 
— Daily  differences. — Range  of  the  tide. — "  Establishment  of  the  Port." — 
"Priming"  and  "lagging"  of  the  tides. — Equinoctial  tides. — Tides  at 
the  solstices. — Tidal  irregularities  of  various  kinds. — In  and  around 
Great  Britain. — Amongst  the  South  Sea  Islands. — Influence  of  the  baro- 
meter.— Journey  of  the  tidal  wave  round  the  Earth. — The  "  Bore." 

pp. 41-54 


CHAPTER  V. 
THE  PLANETS  GENERALLY. 

What  the  planets  are. — May  be  conveniently  divided  into  two  groups. — 
The  Inferior  Planets. — The  Superior  Planets. — The  Minor  Planets. 
— Certain  planets  have  satellites. — The  purpose  served  by  them. — Certain 
planets  have  phases. — The  planets  in  Conjunction. — The  planets  in 
Opposition. — Transits  across  the  Sun. — Characteristics  common  to  all 
the  planets. — Statement  of  these  by  Hind. — Kepler's  Three  Laws. — Sir  J. 
HerscheVs  statement. — Conjunction  of  two  planets. — Instances  of  this. — 
Various  discarded  planetary  systems. — Suggested  I ntr a- Mercurial  and 
Trans- Neptunian  planets.  .  pp.  55-66 


CONTENTS.  XI 

CHAPTER  VI. 

THE  MOST   INTERESTING  AND   FAMILIAR 
PLANETS. 

A  classification  of  the  planets, — Mercury. — Difficult  to  observe. — 
Spots. — Phases. — Schiaparelli's  observations.  — Axial  rotation. — Sta- 
tistics. — How  to  find  Mercury  or  Venus. — Venus. — Movements  resem- 
ble those  of  Mercury. — Physical  features. — Possible  mountains. — At- 
mosphere.— A lleged  satellite. — Phases. — Galileo's  anagram. — Statistics. 
— Mars. — The  Earth's  nearest  neighbour. — Celebrated  for  its  colour. — 
Subject  to  a  slight  phase. — This  planet  very  accessible  for  observation. 
— Its  apparent  movements. — Physical  appearance. — Much  controversy  as 
to  this. — Polar  snows. — Spots. — Markings  very  permanent. — Its  colour. 
— Satellites. — Statistics. — Jupiter. — Easy  of  observations. — The  largest 
planet. — Belts. — Spots. — Jovian  spots  and  Sun-spots. — Satellites. — 
Large  ones  easily  found  and  followed. — Small  ones  very  difficult. — Pheno- 
mena.— Velocity  of  light. — Statistics. — Saturn. — Its  rings. — General 
description  of  them. — How  designated. — Changes  in  the  appearance  of 
the  rings  from  time  to  time. — Some  details  respecting  them. — The  ball. — 
The  satellites  as  tests  for  telescopes. — Statistics.  .  .  pp.  67-97 


CHAPTER  VII. 
THE  LESS  KNOWN  PLANETS. 

The  planets  of  this  chapter  of  little  interest  to  the  amateur. — History  of 
the  discovery  of  Uranus. — Difficulties  as  to  its  orbit. — Suspicions  of  the 
orbit  being  disturbed  by  another  planet. — The  search  for  it. — The  re- 
searches of  Adams  and  Leverrier. — The  discovery  of  Neptune. — Brief 
description  of  the  planet. — 7/s  one  satellite. — TheMinor  Planets. — First  or- 
ganised search  for  them. — Early  discoveries. — Recent  discoveries  facilitated 
by  photography. — The  planets  now  very  numerous. — And  few  of  them  of 
any  interest. — Their  fantastic  names. — Some  particulars  of  the  first 
four. — Summary  respecting  their  orbits  .  .  .  pp.  98-112 


CHAPTER  VIII. 
ECLIPSES. 

The  principles  of  eclipses. — Other  kindred  phenomena. — Two  anec- 
dotes.— The  difference  between  eclipses  of  the  Sun  and  of  the  Moon. — Total 
eclipses. — Partial  eclipses. — Annual  number  of  eclipses. — The  Saros. — 
Method  of  using  the  Saros. — Eclipses  of  the  Sun  considered. — The  accom- 
paniments of  a  large  partial  eclipse  of  the  Sun. — Of  a  total  eclipse. — The 
terror  of  savages. — Instances  of  this.. — The  darkness. — The  fall  of  tempera- 


Xll  CONTENTS. 

ture. — The  red  flames. — Baily's  Beads. — The  Corona. — Details  relating 
thereto. — The  Moon's  shadow. — Shadow-bands. — Bushes  of  light. — The 
Corona,  a  solar  appendage. — Connection  between  its  shape  and  spots  on 
the  Sun. — Coming  eclipses. — Eclipse  expeditions. — Eclipses  of  the 
Moon. — The  Moon  when  totally  eclipsed. — Anecdote  of  Columbus. — In- 
cident in  the  South  African  War. — Transits  of  Mercury  and  Venus. — 
Method  of  measuring  the  Sun's  distance. — Transits  and  eclipses  of  the 
satellites  of  Jupiter. — Occultation  of  planets  and  stars  by  the  Moon. — 
Occupation  of  stars  and  planets  by  planets  .  .  .  pp.  113-143 

CHAPTER  IX. 
COMETS, 

Always  objects  of  popular  interest. — Very  numerous. — Telescopic  comets. 
— Great  comets  visible  to  the  naked  eye. — Changes  in  the  appearance  of 
a  comet  after  its  first  discovery. — Often  easily  mistaken  for  a  nebula. — 
Usual  changes  exhibited  by  a  telescopic  comet. — Become  visible  as  they 
approach  the  Sun. — What  is  a  comet's  tail  ? — Where  does  it  come  from  ? — 
Why  do  some  comets  have  tails  and  not  others  ? — These  questions  difficult 
to  answer. — Sir  J .  Herschel's  opinion. — General  account  of  tails. — Some 
tails  probably  cylindrical. — Bredichen's  Types  of  tails. — The  '"Light- 
pressure"  theory. — Orbits  of  comets. — Periodical  comets. — Celebrated 
comets. — Some  statistics  .«»...  pp.  144—171 

CHAPTER  X. 
SHOOTING-STARS. 

Various  classes  of  luminous  meteors. — Shooting- stars. — Fireballs. — 
Aerolites. — Radiant  points  of  shooting-stars. — Account  of  the  most  im- 
portant showers. — Position  in  the  heavens  of  some  of  the  chief  radiant 
points. — Historical  allusions. — Celebrated  great  showers. — Fireballs. — 
Their  general  resemblance  to  one  another. — Remarkable  fireballs  described 
by  Webb  and  Brodie. — Their  sizes,  distances,  and  movements. — Compu- 
tation of  their  paths. — Connection  between  meteors  and  comets. — Shooting- 
stars,  fireballs,  and  aerolites  all  of  the  same  nature. — Circumstances  attend- 
ing the  fall  of  aerolites  pp. 172-190 


CHAPTER  XI. 
THE  STARS. 

The  apparent  movement  of  the  stars  on  a  starlight  night. — The  stars 
in  magnitudes. — Diurnal  movement  of  the  Earth. — Its  consequences. — 
The  stars  visible  vary  with  the  latitude. — The  expression  "  fixed 


CONTENTS.  xiii 

Stars  that  art  visible  to  the  naked  eye. — The  identification  of  the  stars, 
— Bayer's  system  of  lettering  stars. — Flamsteed's  numbers. — Sir  J. 
HerscheVs  striking  remarks. — Total  number  of  naked- eye  stars. — Amount 
of  star-light. — Twinkling. — Double  stars. — Binary  stars. — Coloured 
stars. — Complementary  colours. — Triple  and  multiple  stars. —  Variable 
stars. — Notable  variable  stars. — Temporary  stars. — Tycho  Brake's  Star. — 
Recent  temporary  stars  ......  pp.  191-225 


CHAPTER  XII. 
GROUPS  OF  STARS  AND  NEBULAE. 

Stars  in  groups  classified. — Irregular  groups. — Clusters  of  stars  more 
or  less  compressed. — Nebulce. — Classification  of  nebulce. — Annular 
nebula. — Elliptic  nebulce. — Spiral  nebulce. — Planetary  nebula. — 
Nebulous  stars. — Large  nebulce  of  irregular  form. — Exemplification  of 
these  classes  named. — Distribution  of  nebulce  and  clusters  over  the  heavens. 
— The  Milky  Way. — Brief  description  of  its  position. — Its  historic  names. 

pp. 226-243 

CHAPTER  XIII. 
THE  CONSTELLATIONS. 

The  subject  one  of  great  interest. — The  best  way  of  learning  their  posi- 
tions.— The  effects  of  the  diurnal  movement. — Star-atlases  and  plani- 
spheres.— The  constellations  best  learnt  in  the  open  air. — List  of  stars  of 
the  ist  magnitude. — Standard  stars  of  the  first  4  magnitudes. — Alignment 
of  stars. — Origin  of  the  constellations. — Modern  additions. — A  hasty 
survey  of  the  Northern  Hemisphere  .  .  .  .  pp.  244-255 


CHAPTER  XIV, 
TELESCOPES. 

Telescopes  are  of  two  kinds. — Reflectors,  Refractors. — Various  kinds  of 
reflectors. — Brief  description  of  each. — Principle  of  a  refractor. — Spherical 
aberration. — Chromatic  aberration. — The  opera-glass. — Stands  for  tele- 
scopes.— Importance  of  a  good  stand. — Equatorial  stands. — Advantages  of 
an  equatorial  mounting. — Accessories  to  a  telescope. — Driving-clock. — 
Sidereal-clock. — The  housing  of  a  telescope. — Advantages  of  an  observa- 
tory.— Detailed  description  of  how  to  bmld  one  .  .  .  pp.  256-282 


XIV  CONTENTS. 

CHAPTER  XV. 
TIME  AND  ITS  MEASUREMENT, 

Years. — Months. — Weeks. — Days. — Hours. — The  Sidereal  Year. — The 
Mean  Solar  Year. — The  Anomalistic  Year. — Hipparchus. — The  Calendar 
and  the  reforms  it  has  undergone. — By  Julius  Casar. — By  Pope  Gregory 
XIII. — His  Calendar  adopted  by  England. — But  not  by  Russia. — ' '  Old 
Style." — "New  Style." — The  Lunar  Month. — The  week. — Quotation 
from  Laplace. — Savages  count  time  by  "  Moons." — Divisions  of  the  Day. 
— The  24-hour  Day. — a.m.  and  p.m. — Railway  time. — The  "  Prime 
Meridian." — Greenwich  chosen  for  this. — Standard  time. —  Usage  of 
different  nations. — Where  does  the  day  begin  ? — The  Transit  Instrument 
and  how  to  use  it  for  obtaining  the  time  ....  pp.  283-300 

CHAPTER  XVI. 
THE  SPECTROSCOPE   ASTRONOMICALLY. 

What  is  a  spectrum  ? — The  decomposition  of  sunlight. — Brief  history 
of  the  application  of  prisms  to  sunlight. — Labours  of  Grimaldi. — Of  Sir 
7.  Newton. — Of  Wollaston. — Of  Fraiinhofer. — The  lines  in  the  spectrum 
named  by  him. — And  after  him. — Some  details  as  to  these. — Their  inter- 
pretation.— The  labours  of  Huggins  and  others. — Application  of  the 
spectroscope  to  celestial  objects. — Secchi's  star  types. — Motions  of  the  stars 
as  ascertained  by  the  spectroscope  ...  .  pp.  301-309 

CHAPTER  XVII. 

TABLE  OF  THE  CONSTELLATIONS,  WITH  A 
BRIEF  DESCRIPTIVE  ACCOUNT  OF  EACH  pp.  310-322 

APPENDIX  I. 

STATISTICS  RESPECTING  THE  PLANETS  AND 
THEIR  SATELLITES pp.  323-324 

APPENDIX  II. 

CATALOGUE  OF  CELESTIAL  OBJECTS  EASY  FOR 
SMALL  TELESCOPES pp.  325-328 

INDEX    .  pp.  329-335 


LIST   OF   ILLUSTRATIONS. 

COLOURED    PLATES. 

1C. 

i  THE  PLANET  SATURN  (Boltori)  .         .   PLATE  I   Frontispiece 

PLATE  PAGE 

iooa  MARS  (Boltori)         .          .     .,    .          .          .  XXIXA  .  80 

108  JUPITER  (Bolton)      .  XXXII  .  84 

141,  1410  PROMINENCES  OH  THE  SUN       .          .  XXXVII  .  114 

162  TOTAL  ECLIPSE  OF  THE  MOON  (Tempel)        .  XLVIII  .  138 

258  DAYLIGHT  METEOR  (/.  Nasmyth)        .         .  LXXXIII  .  188 

262  COLOURED  STARS LXXXIV  .  208 

263  COLOURED  STARS      .....  LXXXV  .  210 

BLACK-AND-WHITE  ILLUSTRATIONS. 

2.  East  Indian  Coral              .......  8 

3.  Spot  on  the  Sun,  Aug.  14,  1868 n 

4.  A  Typical  Sun-spot  (S.  P.  Langley)     ...           II     .  12 

5.  The  Disc  of  the  Sun,  showing  Spots,  Oct.  22, 

1905  (Barlow)        ....  Ill     .     i2a 

6.  The  Disc  of  the  Sun,  showing  Spots,  July  31, 

1906  (Barlow)        ...  ,,  i2a 

7.  The  Disc  of  the  Sun,  showing  Spots,  Feb.  7, 

1907  (Barlow)        ......  ,,  i2a 

8.  The  Disc  of  the  Sun,  showing  Spots,  May  6, 

1907  (Barlow)        ......          ,,  iza 

9.  The  Disc  of  the  Sun,  showing  Spots,  July  15, 

1907  (Barlow) IV     .     126 

10.  The  Disc  of  the  Sun,  showing  Spots,  May  4, 

1908  (Barlow) ,,       .     I2& 

11.  The  Disc  of  the  Sun,  showing  Spots,  Aug.  3, 

1908  (Barlow)        .          .  .          .  „       .     I2& 

12.  The  Disc  of  the  Sun,  showing  Spots,  Sept.  2, 

1908  (Barlow) ,,       .     126 

13.  The    Great    Sun-spot  of  1865   on  Oct.   14 

(Hewlett)      .....  .  V     .       13 

14.  The   Great   Sun-spot   of   1865   on  Oct.    16 

(Howlett} „     .       13 


XVI 


LIST    OP    ILLUSTRATIONS. 


FIG.  PLATE  PAGE 

15.  The  Great  Sun-spot  of  1865  disappearing  on 

Nov.  3  (Howlett)   .          .          .          .     "     .          .  V      .  13 

16.  Remarkable  Sun-spot,  Oct.  20,  1905  (Bar- 

low)    .          .                     VI      .  14 

17.  Granulations  and    Faculas,   Nov.   16,    1905 

(Barlow)      .......  ,,       .  14 

18.  Large   Compact    Sun-spot,   June   22,    1889 

(McK.) 14 

19-26.  Sun-spots  in  1882  at  various  dates 

(Cortie) VII  .  15 

27—30.  The  Great  Sun-spot  of  Feb.  1905  at 

various  dates  ......  VIII      .  18 

31-35.  Changes  in  Sun-spots  as  they  approach 

the  Sun's  Limb :  exemplified  in  May 

1906  (Barlow)  .          .          .          .          .          .  IX      .  19 

36.  Facula?  on  the  Sun,  June  28,  1884  (Cortie)  .          .  X      .  22 

37.  Faculoe  on  the  Sun,  Nov.  28,  1884  (Cortie)  .          .  ,,      .  22 

38.  The  Red  Sunsets  in  1883 XI      .  23 

39.  Map  of  the  Moon      ......  XII      .  26 

40.  The  Phases  of  the  Moon XIII      .  27 

41.  The  Moon's  Surface  in  Model  (Nasmyth)     .          .  XIV     .  28 

42.  The   Lunar  Mountain  Copernicus   (W.  H. 

Pickering) XV     .  29 

43.  The  Mare  Crisium  on  the  Moon  (Weinek)    .          .  XVI      .  30 
44—45.   The    Lunar    Mountain    "  Archimedes," 

1888  (Weinek)           .          .          .          .          .  XVII     .  31 

46-51.    Mountains  on  the  Moon  (Stuyvaert)        .          .  XVIII      .  34 

52-57.    Mountains  on  the  Moon  (Stuyvaert)        .          .  XIX      .  35 

58-63.    Mountains  on  the  Moon  (Stuyvaert)        .          .  XX      .  36 

64-67.    Mountains  on  the  Moon  (Stuyvaert)        .          .  XXI      .  37 

68.  The  Earth-lit  New  Moon.  Feb.  17,  1907      .          .  XXII      .  52 

69.  The    "Bore"    on  the    River  Tsien-Tang- 

Kiang,  China XXIII     .  53 

70.  The  Inclination  of  the  Axes  of  the  Planets  .          .  •        •  •  59 

71.  Diagram  illustrating  Kepler's  Second  Law  .          .  .,          .60 

72.  Conjunction  of  Venus  and  Saturn,  1845       .          .  ...       .  63 

73.  Conjunction  of  Mars  and  the  Moon,  1909   .          .  .          .  64 

74.  Mercury  (Guiot)        ........  69 

75.  Mercury,  Nov.  5,  1881  (Denning)        .          .          .  XXIV     .  72 

76.  Mercury,  Nov.  6,  1881  (Denning)        .          .  ,,           .72 

77.  Mercury,  Nov.  8,  1881  (Denning)        .          .          .  .72 

78.  The  Various  Phases  of  Venus   .                    .          .  XXV     .  73 

79.  Venus  near  its  Inferior  Conjunction  (Schro- 

ter) ,     .  .          .73 

80.  Venus,  Dec.  23,  1885  (Lihou) 73 

81.  Venus,  March  22,  1 881  (Denning)        .          .          .  XXVI      .  76 

82.  Venus,  March  26,  1881  (Denning)       .          .          .  ,,           .  76 

83.  Venus,  March  28,  1881  (Denning)        .          .          .  -76 

84.  Venus,  March  30,  1881  (Denning)  ,,  76 


LIST    OF    ILLUSTRATIONS. 


FIG. 

85.  Venus,  March  31,  1881  (Denning) 

86.  Venus,  April  5,  1881  (Denning) 

87.  Mars,  May  14,  1903  (IV.  F.  Gale) 

88.  Mars,  April  14,  1903  (P.  B.  Molesworth) 

89.  Mars,  April  19,  1903  (T.  E.  R.  Phillips) 
go.  Mars,  April  21,  1903  (P.  B.  Molesworth) 

91.  Mars,  May  21,  1903  (R.  Killip) 

92.  Mars,  April  8,  1903  (H.  Carder) 

93.  Mars,  May  12,  1903  (T.  E.  R.  Phillips) 

94.  Mars,  April  30,  1903  (P.  B.  Molesworth) 

95.  Mars,  March  31,  1903  (E.  M.  Antoniadi) 

96.  Mars,  March  31,  1903  (E.  A.  L.  Attkins) 

97.  Mars,  March  31,  1903  (W.  J.  Hall) 

98.  Mars,  May  7,  1903  (T.  E.  R.  Phillips) 

99.  Mars,  Sept.  20,  1909  (Antoniadi) 

100.  Mars,  Nov.  5,  1909  (Antoniadi) 

101.  Mars  on  Mercator's  Projection  (Antoniadi) 

102.  Jupiter,  Sept.  20,  1879    . 

103.  Jupiter,  Oct.  15,  1879 

104.  Jupiter,  Oct.  14,  1882 

105.  Jupiter,  Dec.  24,  1882     . 

106.  Jupiter,  Nov.  7,  1884 

107.  Jupiter,  Feb.  27,  1885     . 

109.  Jupiter's  Red  Spot,  Nov.  19, 1880  (Denning) 

no.  Jupiter's  Red  Spot,  Sept. 28, 1881  (Denning) 

in.  Jupiter's  Red  Spot,  Dec.  7, 1881  (Denning) 

112.  Jupiter's  Red  Spot,  Oct.  30, 1882  (Denning) 

113.  Jupiter's  RedSpot,  Oct.  15, 1883  (Denning) 

114.  Jupiter's  Red  Spot,  Feb.  6,  1884  (Denning) 

115.  Jupiter's  Red  Spot,  Feb.  25, 1885  (Denning) 

116.  Jupiter's  Red  Spot,  May  9,  1885  (Denning) 
117-128.    Jupiter  with  its  Satellites,  Aug.  21, 

1867  (Tempel) 

129.  Jupiter's  Red  Spot  in  the  i7th  Century 

130.  Saturn,  Jan.  5,  1862  (Wray)     . 

131.  Saturn,  Feb.  to  March  1884  (Henry) 

132.  Saturn,  Feb.  1887  (Terby) 

133.  Saturn,  March  18,  1887  (Elger) 

134.  Saturn,  July  30,  1899  (Antoniadi) 

135.  Saturn,  Jan.  27,  1912  (Phillips) 

136.  Irregularities  in  the  Crape  Ring,  March  21, 

1887  (Elger) 

137.  Irregularities  in  the  Crape  Ring,  March  27, 

1887  (Elger) 

138.  Saturn,  Feb.  7,  1890 

139.  How  Minor  Planets  are  recognised  as  such 

140.  The  Orbits  of  Eros,  Mars,  and  the  Earth 

142.  Solar  Eclipsesvisible  in  England,  1891-1922 

143.  Total  Eclipse  of  the  Sun,  Aug.  7,  1869 

b 


PLATE 

PAGE 

.    XXVI 

.        76 

,, 

.       76 

XXVII 

77 

>orth)    . 

77 

lips)     . 

77 

'orth)    . 

77 

,, 

77 

» 

77 

ips)      .           XXVIII 

.       78 

iorth)    . 

.       78 

liadi)  .                 ,, 

.       78 

kins)    .                 ,, 

.       78 

. 

.       78 

Os)        . 

.       78 

.   XXIX 

79 

79 

oniadi)               XXX 

.        82 

XXXI 

•        83 

» 

•        83 

. 

.        83 

• 

•        83 

. 

•        83 

• 

•        83 

enning)          XXXIII 

86 

enning)                 , 

86 

enning)                 , 

.        86 

enning)                 , 

.        86 

enning)                 , 

.        86 

enning)                 , 

86 

enning)                 , 

86 

enning)                 , 

86 

Ug.    21, 

XXXIV 

.        87 

tury    . 

.       87 

XXXV 

.        92 

) 

92 

92 

XXXVI 

93 

» 

93 

. 

93 

rch  21, 

93 

rch  27, 

. 

93 

. 

•       95 

as  such 

.     109 

Earth  . 

.     in 

1-1922       XXXVIII 
]6g       .          XXXIX 

.      116 
.      117 

LIST   OF    ILLUSTRATIONS. 


MO.  PLATE              FACE 

144.  The  Solar  Corona,  July  29,  1878  (Murphy)         .  XL     .     120 

145.  The  Solar  Corona,  Aug.  29,  1886  (Harvard 

Annals,  xviii.)     ......  XLI      .     121 

146.  The  Solar  Corona,  Dec.  22,  1889  (Perry)  „              121 

147.  The  Solar  Corona,  1898  (C.  M.  Smith)       .          .  XLII     .     124 

148.  The  Solar  Corona,  May  28,  1900       .          .          .  XLIII      .      125 

149.  The  Eclipse  of  the  Sun,  April  17,  1912,  at 

11.46  G.M.T.  (Barlow)           ....  XLIV     .      136 

150.  The  Eclipse  of  the  Sun,  April  17,  1912,  at 

12.5  G.M.T.  (Barlow)             ...  ,,               136 

151.  The  Eclipse  of  the  Sun,  April  17,  1912,  at 

12. 1 1  G.M.T.  (Barlow)            ...  ,,                136 

152.  Total  Eclipse  of  the  Moon,  Jan.  28,  1888  .          .  XLV     .   136*3 

153.  Total  Eclipse  of  the  Moon,  Jan.  28,  1888  ,,             136(3 

154.  Total  Eclipse  of  the  Moon,  Jan.  28,  1888  .          .  XLVI      .   1366 

155.  Total  Eclipse  of  the  Moon,  Jan.  28,  1888  .          .  ,,          .    1366 

156.  Total  Eclipse  of  the  Moon,  Jan.  28,  1888  .          .  XLVII      .     137 
157-160.    Occultation  of  Jupiter  by  the  Moon, 

Aug.  12,  1892  (W.  H.  Pickering]     .          .  ,,           .137 
161.    Diagram    of    the    Corona,   Aug.   8,    1896 

(E.  J.  Stone]        ....  .     137 

163.  Phases  of  the  Transit  of  an  Inferior  Planet          .  .          .     141 

164.  Brooks's  Comet  of  1898  (x.)  on  Nov.  ii    ....     145 

165.  Brooks's  Comet  of  1898  (x.)  on  Nov.  15    .          .  .          .     145 

166.  Diagram    to     show     Recognition     of     a 

Comet        .          .          .          .          .          .          .  .          .     147 

167.  Telescopic  Comet  without  a  Nucleus         ....     149 

168.  Telescopic  Comet  with  a  Nucleus      .          .          .  .          .1/19 

169.  Head  of  Brooks's  Comet,  1884  (i.),  Jan.  13 

(Thollon] XLIX      .     150 

170.  Head  of  Brooks's  Comet,  1884  (i.),  Jan.  19 

(Thollon] ,,          .150 

171.  Encke's  Comet,  Sept.  22,  1848  (Smyth)      .          .  L     .     151 

172.  Medal  of  Comet  struck  in  1680          .          .        >.  *         .     153 

173.  Naked-eye  View  of  Halley's  Comet  in  1910 

(Leon) LI     .     154 

174.  Curious  Aspect  of  Halley's  Comet,  June  8, 

1910  (Leon)          ......  LII      .      155 

175.  The  Great  Comet  of  1 81 1          ....  LIII      .     156 

176.  The  Great  Comet  of  1843  on  March  17      .          .  LIV     .     157 

177.  Donati's  Comet,  Oct.  5,  1858  (Pape)          .          .  LV     .     158 

178.  The' Comet  of  1860  (iii.),  June  26  (Cap- 

pelletti  and  Rosa]           .          .          .          .          .  LVI      .      159 

179.  The  Comet  of  1860  (iii.),  June  28  (Cap- 

pelletti  and  Rosa] „        .      159 

180.  The  Comet  of  1860  (iii.),  June  30   (Cap- 

pelletti  and  Rosa] ,,        .     159 

181.  The    Comet  of   1860    (iii.),  July   i    (Cap- 

pelletti  and  Rosa] „        .     159 


LIST    OF    ILLUSTRATIONS. 

FIG. 

182.   The  Comet  of  1860   (iii.),   July   6   (Cap- 
pelletti  and  Rosa) 
183.   The  Comet   of   1860    (iii.),   July   8    (Cap 
pelletti  and  Rosa) 
184.   The  Comet  Families  of  the  Planets  . 
185.    Halley's  Comet,  May  i,  1910  . 
186.   Halley's  Comet,    1910,  on  May  5   (More- 
house)         ...... 
187.    Halley's  Comet,  1910,  on  May  13  (More- 
house)         ...... 
188.    Halley's  Comet,  1910,  on  May  25  (More- 
house)         ...... 

PLATE 

.       LVI 

!      LVII 
.    LVIII 

xix 

PAGE 

•        159 

•        159 
•        159 
.        162 

•        I63 
•        I63 
163 

189.    Halley's  Comet,   1910,  on  May  29  (More- 
house)          ...... 
190.    Halley's  Comet,  1910,  on  May  30  (More- 

.'•       " 

.        I63 
16^5 

191.    Halley's  Comet,   1910,  on  June  5  (More- 
house)         ...... 
192.    Path  of  Halley's  Comet,  April  1910 
193.   The  Warner  Prize  Medal 
194.   The  Great  Comet  of  1744 
195.    Coggia's  Comet,  1874,  on  July  13  (F.Brodie) 
196.   The  Great  Comet  of  1882  (Charlois) 
197.   The  Great  Comet  of  1882  on  Nov.  7 
198.   The  Great  Comet  of  1882  on  Nov.  13 
199.   The  Head  and  Nucleus  of  the  Great  Comet 
of  1882  on  Nov.  13       . 
200.   The  Head  and  Nucleus  of  the  Great  Comet 

» 

LIX 
LX 
.       LXI 

.     LXII 

.        I63 
•        I63 
.        164 
•       165 

.      1  66 
.   i66a 
.   1666 
.    1666 

.    i66c 
.    i66r 

201.   The  Nucleus  of  the  Great  Comet  of  1882 
on  Feb.  i,  1883  .          .          .          . 
202.   The  Nucleus  of  the  Great  Comet  of  1882 
on  Feb.  23,  1883            .... 

.   LXIII 

.   i66d 
.    i66d 

203.   The  Nucleus  of  the  Great  Comet  of  1882 
on  Feb.  27,  1883            .... 
204.   The  Nucleus  of  the  Great  Comet  of  1882 
on  March  3,  1883           .... 
205.    Swift's  Comet  of  1892  (i.)  on  March  30 
206.    Swift's  Comet  of  1892  (i.)  on  April  5 
207.    Swift's  Comet  of  1892  (i.)  on  April  6 
208.    Swift's  Comet  of  1892  (i.)  on  April  7 

.    LXIV 
!      LXV 

.      167 

.      167 
.      168 
.      168 
.      168 

.      168 

209.    Swift's  Comet  of  1892  (i.)  on  April  14 
210.    Swift's  Comet  of  1892  (i.)  on  April  21 
211.    Swift's  Comet  of  1892  (i.)  on  April  22 
212.    Swift's  Comet  of  1892  (i.)  on  April  23 
213.    Rordame's  Comet  of  1893   (ii.)  on  July  8 
(Hussey)      ...... 
214.    Rordame's  Comet  of  1893  (ii.)  on  July  13 

.    LXVI 
.  LXVII 

.    i68a 
.    i68a 
.    1680 
.    i68« 

.    1686 
,    1686 

XX 

LIST   OF    ILLUSTRATIONS. 

FIG. 

PLATE 

PAGE 

215. 

Brooks's  Comet  of  1893  (iv.),  Oct.  21 

LXVIII 

.    i68c 

216. 

Brooks's  Comet  of  1893  (iv.),  Oct.  22 

f| 

.    i68c 

217. 

Borelly's   Comet    of     1903     (iv.),    (R.    J. 

Wallace]      ...... 

.    LXIX 

.    i68d 

aiS. 

Giacobini's  Comet  of  1906  (i.)  on  Dec.  29, 

1905  (E.  E.  Barnard)    .... 

.      LXX 

.    i68e 

219. 

Giacobini's  Comet  of  1906  (i.)  on  Dec.  29, 

1905  (£.  E.  Barnard)    .          . 

.    LXXI 

.    i68/ 

220. 

Giacobini's  Comet  of  1906  (i.)  on  Jan.  5, 

1906  (E.  E.  Barnard)    .... 

i68/ 

221. 

Daniel's  Comet  of  1907  (iv.)  on  Aug.  18 

" 

(Kennedy)            ..... 

LXXII 

169 

222. 

Morehouse's  Comet  of  1908  (iii.)  on  Oct.  15 

(E.  E.  Barnard)    

LXXIII 

170 

223. 

Morehouse's  Comet  of  1908  (iii.)  on  Oct.  15 

(Yerkes  Observatory)      .... 

LXXIV 

.   i7oa 

224. 

Morehouse's  Comet  of  1908  (iii.)  on  Nov.  15 

(  Yerkes  Observatory)      .... 

n 

.    i7oa 

225. 

Morehouse's  Comet  of  1908  (iii.)  on  Nov.  13 

.  LXXV 

.    170^ 

226. 

Halley's  Comet,  1910,  on  May  25  (Gingrich) 

LXXVI 

.    170^ 

227. 

Halley's  Comet,  1910,  on  May  27  (Gingrich) 

M 

.    i7oc 

228. 

Halley's  Comet,  1910,  on  May  28  (Gingrich) 

t| 

.    i7oc 

229. 

Halley's  Comet,  1910,  on  June  2  (Gingrich) 

>f 

'  .    1700 

230. 

The  Daylight  Comet  of  1911  (W.  B.  Gibbs) 

LXXVII 

.   170^ 

231. 

Brooks's  Comet  of  1911  on  Sept.  21  (Long- 

bottom)        ...... 

LXXVIII 

•      I7i 

232. 

Brooks's  Comet  of  1911  on  Sept.  24  (Long- 

bottom)        ...... 

.      171 

233- 

A  Meteor  in  Flight  (E.  E.  Barnard) 

LXXIX 

.      172 

234- 

Fishing  for  Meteors  (Longbottom) 

LXXX 

•      173 

235- 

Flight  of  Telescopic  Meteors  (Brooks)       "* 

. 

•      173 

236. 

Meteor  Radiant  Point  in  Gemini 

.      177 

237- 

Meteor  Radiant  Point  in  Leo  . 

LXXXI 

.      178 

238. 

Meteor  seen  on  Nov.   14,  1868,  at  New- 

haven,  Conn.,  U.S.,  at  1.15  a.m.    . 

LXXXII 

.      179 

239- 

Meteor  seen  on  Nov.   14,   1868,   at  New- 

haven,  Conn.,  U.S.,  at  1.19  a.m.    . 

it 

.      179 

240. 

Meteor  seen  on  Nov.   14,   1868,   at  New- 

haven,  Conn.,  U.S.,  at  1.30  a.m.     . 

() 

•      179 

241. 

Meteor  seen  on  Nov.   14,  1868,   at  New- 

haven,  Conn.,  U.S.,  at  1.39  a.m.    . 

M 

•      179 

242. 

Meteor  seen  on  Nov.  14,  1868,  at  Palisades, 

N.Y.,  at  1.14  a.m  

179 

243- 

Meteor  seen  on  Nov.  14,  1868,  at  Palisades, 

N.Y.,  at  1.18  a.m  

?> 

.      179 

244, 

Meteor  seen  on  Nov.  14,  1868,  at  Palisades, 

N.Y.,  at  i.  21  a.m.         .... 

|f 

.      179 

245^ 

Meteor  seen  on  Nov.  14,  1868,  at  Palisades, 

N.Y.,  at  1.28  a.m.         .          . 

,, 

.      179 

LIST   OF    ILLUSTRATIONS. 

FIG.  PLATE 

246.  Meteor  seen  on  Nov.  14,  1868,  at  Haver- 

ford,  Pa LXXXII 

247.  Meteor  seen  on  Nov.  14,  1868,  at  Williams- 

town,  Mass.,  at  1.15  a.m.       ...  „ 

248.  Fireball  of  Aug.  1 8,  1783  (first  view) 

249.  Fireball  of  Aug.  18,  1783  (second  view)     . 

250.  Fireball  of  June  7,  1878  (Denning)  .     '     . 

251.  Fireball  of  Oct.  19,  1868  (Schmidt)  . 

252.  Fireball  of  Oct.  19,  1877  (first  effect) 

253.  Fireball  of  Oct.  19,  1877  (second  effect)     . 

254.  Successive  Changes  in  a  Fireball    (three 

views)          ........ 

255.  Meteor  of  Nov.  12,  1861  (Webb)         .... 

256.  Fireball  observed    in  the   Isle  of  Wight, 

Feb.  22,  1909  (C.  G.  Brodie)  .... 

257.  Orbit  of  the  Leonids  and  of  the  Comet  of 

1866  (i.) 

259.  Apparent    Changes    in    Stars  rising   and 

setting        ........ 

260.  An  Apparent  Double  Star         ..... 

261.  Diagram   for    plotting    Measurements    of 

Double  Stars 

264.  Light-curve  of  the  Variable  Star  T  Cassi- 

opeiae          ......... 

265.  Light-curve  of  the  Variable  Star  S  Cassi- 

opeia         .  ..... 

266.  Light-curve  of  the  Variable  Star  R  Auriga3 

267.  Light-curve  of  the  Variable  Star  R  Ursa 

Majoris       ........ 

268.  Light-curve  of  the  Variable  Star  T  Ursae 

Majoris      ........ 

269.  Light-curve  of  the  Variable  Star  S  Ursae 

Majoris       ........ 

270.  Light-curve  of  the  Variable  Star  S  Bootis  . 

271.  Light-curve  of  the  Variable  Star  R  Came- 

lopardi        ........ 

272.  Ligh  t-curve  of  the  Variable  Star  RDraconis 

273.  Light-curve  of  the  Variable  Star  T  Cephei 

274.  Light-curve  of  the  Variable  Star  S  Cephei 

275.  Light-curve  of  the  Variable  Star  R  Cassi- 

opeiae          ........ 

276.  Light-changes  in  Nova  Persei,  1901 

277.  Tycho  Brahe's  Mural  Quadrant         .... 

278.  The  Pleiades  (Tempel)     ....        LXXXVI 
279-    Nebulas  in  the  Pleiades  (/.  Roberts)  .          .      LXXXVII 

280.  The  Cluster  13  M.  Herculis  (W.  E.  Wilson)    LXXXVIII 

281.  The  Cluster  u>  Centauri    ....        LXXXIX 

282.  The  Cluster  47  Toucani XC 

283.  The  Cluster  2  M  Aquarii  (Sir  /.  Herschel)  .          .       XCI 


XXI 

PAGE 
179 
179 

179 
179 
179 

179 
1 80 
180 

181 
182 

183 

187 

193 
205 

207 
213 

213 
213 

213 
215 

215 
215 

215 
217 
217 
217 

217 
219 

221 
226 
227 
228 
229 
230 
231 


XX11 


LIST    OF    ILLUSTRATIONS. 


FIG. 
284. 

285. 
286. 

287. 
288. 
289. 

The  Cluster  5  M  Libras  (Sir  J.  Herschel)     . 
The  Cluster  2  M  Aquarii  (Earl  of  Rosse)     . 
The    Clusters    33   and  34    Ijl    VI    Persei 
(Rambaut)  ...... 
The  Great  Nebula  in  Andromeda  (Shepslowe) 
The  Spiral  Nebula  51  M  Can.  Yen.  (Smyth) 
The  Spiral  Nebula  51  M  Can.  Yen.  (Sir  J. 
Herschel)    

PLATE 

.       XCI 

.      XCII 
.    XCIII 
.     XCIV 

PAGE 

.    231 
.    231 

.    232 

.    232« 

.    2326 

2326 

290. 

The  Spiral  Nebula  in  Ursa  Major  (Shepstowe) 

.     xcv 

•    233 

291. 

The  Nebula  4620  h  Cygni  (Barnard) 

.    XCVI 

•    234 

292. 

The  Nebulae  81  and  82  M   Ursae  Majoris 

(/.  Roberts)           

.  XCVII 

•    235 

293- 

Planetary   Nebula    97    M    Ursge    Majoris 

(Sir  J.  Herschel)     ' 

. 

•    235 

294. 

Planetary  Nebula  97  M  Ursa?  Majoris  (Earl 

of  Rosse)     ...... 

•    235 

295- 

The  Great  Nebula  in  Orion  (Harvard) 

'xcvhi 

.    236 

296. 

The  Great  Nebula  in  Orion  (W.  E.  Wilson) 

.    XCIX 

.    237 

297. 

The  Trapezium  of  Orion 

. 

•    237 

298. 

The  Nebula  surroundings  Argus  (C.E.  Peek] 

c 

.   238 

299. 

The  Nebula  surrounding  17  Argus 

CI 

.    230 

300. 

The  Nebula  17  M  Clypei  Sobieskii    . 

•    239 

301. 

The  Dumb-bell  Nebula  in  Vulpecula  (low 

power)        ...... 

CII 

.    240 

302. 

The  Dumb-bell  Nebula  in  Vulpecula  (en- 

larged)          

• 

.    240 

303. 

The  Dumb-bell  Nebula  in  Vulpecula  (Smyth) 

.     cm 

.   24oa 

304- 

The  Dumb-bell  Nebula  in  Vulpecula  (Earl 

of  Rosse)      ...... 

. 

.   2400 

305' 

Nebulous   Region  of    p  Ophiuchi  (E.   E. 

Barnard)     ...... 

.        CIV 

.   2406 

306. 

Nebulous  Region  of  y  Cygni  (E.  E.  Barnard) 

. 

.   2406 

307. 

The  Nebula  14   Itl  V  Cygni  (Lick  Obser- 

vatory)        ...... 

.  -•     cv 

.    240C 

308. 

The  "  Trifid  Nebula  "  in  Sagittarius 

.       CVI 

.   240^ 

309- 

The  "Trifid  Nebula  "  in  Sagittarius 

.      CVII 

.    240^ 

310. 

Stars  in  Cygnus  (Henry) 

.    CVIII 

.    2407 

3*1- 

The  Nubecula  Major       .... 

CIX 

•   240.? 

312. 

The  Nubecula  Minor     . 

ex 

.  2  40  h 

3I3- 

The  Double  Cluster  in  Perseus 

CXI 

.     241 

3I4- 

Void  space  in  Sagittarius 

.     241 

3I5- 

Kullmer's  "  Star-finder  " 

•     247 

3l6. 

"  Pillar-  and-Claw  "  Stand 

.     261 

317. 
318. 

3-inch  Portable  Equatorial  Telescope 
Old-fashioned  EnglishEquatorial,  circaUgo 

'.      CXTI 

•     263 
.     264 

3*9- 

lo-inch  Equatorial  Telescope  (Cooke) 

.    CXIII 

•     265 

320. 

Standard  Photographic  Equatorial  (Grubb) 

.    CX  IV 

.     266 

321. 

Vienna  2  7-  inch  Refractor  (Grubb) 

.     cxv 

.     267 

322. 

Eye-end  of  the  Vienna  Refractor  (Grubb)  . 

.    CXVI 

.     268 

LIST  OP  ILLUSTRATION 

s. 

xxni 

FIO. 

PLATE 

PAGE 

323.   so-inch  Refractor  of  the  Pulkova  Observa- 

tory (Repsold)      

.  cxvn 

.     269 

324.    Photographic  Equatorial  of  the  Radcliffe 

Observatory,  Oxford   .... 

CXVIII 

.    270 

325.    Siderostat  Equatorial   of    the   Cambridge 

University            ..... 

rt 

.    270 

326.  36-inch  Refractor  of  the  Lick  Observatory 

(Warner  &  Swasey)       .... 

.    CXIX 

.    271 

327.    36-inch  Refractor  of  the  Lick  Observatory 

(another  view)     ..... 

.    cxx 

.     274 

328.    Eye-end  of  the  Lick  Refractor 

.    CXXI 

.  2740 

329.    Distant  View   of    the    Lick   Observatory 

(H.  E.  Mathews)            .... 

.  CXXII 

.  274& 

330.   The  Dearborn  Observatory,  Chicago 

CXXIII 

•     275 

331.    Equatorials    under    Construction    at    the 

Dublin  Works,  1912  (Grubb)  . 

CXXIV 

.   276 

332.    Wooden  Frame  work  of  an  Observatory  Roof 

.  cxxv 

.     277 

333.   The     "  Lethen     Grange  "      Observatory, 

Sydenham            ..... 

277 

334.    Royal  Observatory,  Cape  Town  (Grubb)     . 

CXXVI 

.  278 

335.    Papier-mache  Dome   on    an  Iron-framed 

Observatory  (Grubb} 

278 

336.    Barcelona  University  Observatorv  (Grubb) 

" 

.    278 

337.   Calton  Hill  Observatory,  Edinburgh  (Grubb) 

•           » 

.  278 

338-40.    Observatory   fitted    with    Rising    and 

Falling  Floor  ;  3  positions  (Grubb) 

CXXVII 

.     279 

341.    Sir    W.    Peek's     Observatory,    Rousden, 

Devonshire           ..... 

CXXVIII 

.     280 

342.   Mr.   J.  Tebbutt's  Observatorv,  Windsor, 

N.S.W  

.     280 

343-   The  Imperial  Observatory,  Vienna  , 

CXXIX 

.     281 

344.  Telescope   at   the  Treptow  Observatory, 

Berlin          

.  cxxx 

.     282 

345.   4-ft.  Reflectorof  the  Melbourne  Observatory 

• 

.     282 

346.   28-inch  Refractor  of  the  Greenwich  Obser- 

vatory        ...... 

CXXXI 

.     283 

347.   Meridian  Circle,  U.S.  Naval  Observatory, 

Washington          ..... 

J 

.     283 

348.   Time  all  over  the  World 

.     291 

349.   The  Transit  Instrument 

•     295 

350.    Venus  and  a  Star  in  a  Transit  Instrument 

.     297 

351.    Diagram  to  represent  the  Equation  of  Time 

.     299 

352.    Secchi's  Types  of  Stellar  Spectra 

.     307 

353.   Central  Portion  of  Orion  (Longbottom) 

CXXX1I 

•     314 

354.    "  The  Sickle  "  in  Leo      .... 

CXXXIII 

•     315 

355.   The  Constellation  Orion 

•     315 

356.   The  "  Southern  Cross  "  . 

CXXXIV 

.     316 

357-   The  Spiral  Nebula,  57  M  Canum  Venati- 

corum  (Earl  of  ftosse) 

cxxxv 

.     3i7 

THE    GREEK   ALPHABET 


*«*  The  small  letters  of  this  alphabet  are  so  frequently  emp'oyed  in 
Astronomy  that  a  tabular  view  of  them,  together  with  their  pronunciation, 
will  be  useful  to  many  unacquainted  with  the  Greek  language. 


a  Alpha. 
0  Beta. 
y  Gamma. 
8  Delta, 
e  Epsilon. 
C  Zeta. 
rj  Eta. 
6  Theta. 
t   Iota. 
K  Kappa. 
X  Lambda. 
/A  Mu. 


v  Nu. 
£Xi. 

o  O- micron, 
TT  Pi. 
p  Rho. 
or  Sigma. 
r  Tau. 
v  Upsllon. 
<f)  Phi. 
X  Chi. 
^  Psi. 
co  O-mega 


ASTRONOMY. 

CHAPTER    I. 
INTRODUCTION. 

The  scope  of  the  Science  of  Astronomy. — Its  modern  dev  elopement.— 
The  other  sciences  which  come  in  contact  with  it. — The  resulting 
necessity  of  keeping  the  treatment  of  the  science  within  defined 
limits. — The  different  divisions  of  pure  astronomy. — Mathematical 
Astronomy. — Lord  Grimthorpe's  book,  "Astronomy  without  Mathe- 
matics."— Theoretical  Astronomy. — Descriptive,  or  Visual  Astronomy. 
— Practical  Astronomy. — Amateurs  may  dispense  with  know- 
ledge of  mathematics  altogether  and  of  the  theory  of  telescopes 
and  optics  in  part. — The  modern  application  of  the  spectroscope. 

THE  word  "astronomy,"  coming  as  it  does  from  two  Greek 
words  which,  in  combination,  represent  the  idea  of  "  the  Laws 
of  the  Stars,"  fails  altogether  to  indicate  especially  the  modern 
scope  of  the  science  with  which  it  professes  to  deal.  The  fact 
is  that  the  discoveries  of  modern  times,  which  supplement  the 
astronomy  known  to  the  people  who  lived  a  century  or  two  ago, 
have  extended  it  into  so  many  other  fields  of  knowledge  that 
it  is  not  altogether  easy  always  to  say  where  astronomy,  pure 
and  simple,  ends  and  something  else  begins.  The  chemist, 
the  photographer,  the  optician,  and  to  some  extent  the  geo- 
logist, are  all  concerned,  or  consider  themselves  concerned,  in 
the  sphere  which  formerly  was  limited  to  pure  astronomy, 
being  the  Sun,  Moon,  Planets,  Comets,  and  Stars,  and  the 
phenomena  strictly  connected  with  and  arising  out  of  the  study 
of  these  various  celestial  objects. 
I 


2         ,.    l  r    '  ;    -INTRODUCTION. 

It  will  be  my  endeavour  in  the  following  pages  to  keep  as 
closely  as  I  reasonably  can  to  astronomy  in  its  older  and  more 
limited  sense,  because  were  I  to  attempt  to  draw  into  the 
astronomer's  net  everything  which,  by  modern  custom  or  prac- 
tice, comes  over  the  border-line,  this  book  might  be  open  to  the 
objection  that  it  comprised  too  much  of  everything  and  not 
enough  of  anything. 

The  Science  of  Astronomy,  taken  as  a  whole,  itself  embodies 
several  distinct  lines  of  thought  and  treatment.  One  of  these 
may  be  termed  Mathematical  Astronomy,  and  perhaps  it  may 
be  said  that  it  is  this  subdivision  which  is  most  generally 
assumed  by  people  who  have  not  looked  into  details  to  be  the 
cardinal  feature  of  the  science,  and  therefore  the  one  which 
comes  first  into  the  mind  of  the  general  reader  as  the  dominant 
character  of  the  science.  This  explains  the  fact  that  often 
when  I  have  recommended  the  study  of  astronomy  to  persons 
who  have  never  thought  much  about  the  matter,  I  have  been 
met  with  remarks  couched  more  or  less  as  follows  :  "  Yes,  I 
dare  say  it  is  an  interesting  subject,  but  it  is  too  mathematical 
for  me,  and  I  know  nothing  of  mathematics."  All  this  is,  in 
a  sense,  fallacious.  Whilst  it  is  perfectly  true  that  a  professed 
student  who  wishes  to  get  up  the  subject  to  the  fullest  extent 
must  be  of  a  mathematical  turn  of  mind,  and  be  prepared  to 
go  through  to  the  highest  mathematics,  it  is  a  very  great 
mistake  to  suppose  that  unless  this  is  done  it  is  no  good  taking 
up  the  subject  at  all.  The  view  which  I  am  now  presenting  is 
not  novel,  for  a  great  many  years  ago  the  late  Lord  Grim- 
thorpe,  when  he  was  plain  Mr.  Beckett-Denison,  Q.C., 
published  a  very  useful  little  book  with  the  pointed  title  of 
"Astronomy  without  Mathematics/'  Perhaps  in  some  general 
sense  the  reader  will  find  that  I  have  trodden  in  the  footsteps 
of  my  departed  friend,  but  nobody  could  possibly  assimilate 
Lord  Grimthorpe's  style  and  language,  which  was  completely 
sui  generis  in  every  sense  of  those  useful  words. 

Mathematical   Astronomy   may  otherwise  be  spoken  of  as 


DIFFERENT   BRANCHES   OF   ASTRONOMY.  3 

Theoretical  Astronomy,  because  it  covers  the  theories  of  the 
movements  of  such  of  the  heavenly  bodies  as  move,  and  the 
laws  which  govern  their  movements,  and  so  enables  the  advanced 
students  and  professors  to  predict  with  precision  and  detail  the 
motions  of  the  planets  and  other  moving  bodies  whose  positions 
in  the  sky  from  day  to  day  and  month  to  month  and  year  to 
year  are  set  out  in  our  almanacs. 

In  a  measure  independent  of  this,  we  have  what  may  be 
called  Descriptive,  or  Visual  Astronomy.  This  represents,  with 
respect  to  the  heavens,  the  work  done  by  the  newspaper  re- 
porter and  the  illustrated  newspaper  with  regard  to  things 
mundane.  In  other  words,  the  student  of  astronomy  who 
concentrates  his  attention  on  the  descriptive  side  spends  his 
time  in  using  his  eyes  to  see  what  he  can  see,  and  to  draw 
with  his  pencil  or  record  with  his  camera  what  he  has  seen, 
and  perhaps  to  commit  to  writing  his  observations  for  the  use 
either  of  himself  or  of  somebody  else.  It  is  obvious  that  this 
is  the  popular,  everyday  side  of  the  subject,  and  that  people 
with  fairly  good  eyes  and  a  certain  amount  of  common  sense 
and  intelligence  can  study  the  celestial  bodies  with  pleasure 
and  profit,  even  although  they  know  little  or  nothing  of  mathe- 
matical astronomy,  and  have  no  great  acquaintance  with  the 
third  leading  subdivision  of  the  science  which  is  called 
Practical  Astronomy. 

Practical  Astronomy  deals  with  instruments,  processes,  and 
methods — with  the  principles,  the  construction,  and  the  use 
of  telescopes,  the  construction  and  use  of  star-maps,  the 
instrumental  measurement  of  angles  and  distances,  and  the 
tabulation  of  observations  and  the  drawing  of  conclusions  from 
them. 

As  in  the  former  case  a  student  may  do  a  good  deal  of  useful 
work  with  his  eyes  without  troubling  himself  much  or  at  all 
with  mathematics,  so  also  he  can  do  useful  work,  and  derive 
pleasure  from  it,  in  connection  with  descriptive  astronomy, 
using  th  telescope  to  help  him.  And  this,  though  he  knows 


4  INTRODUCTION. 

little  or  nothing  about  the  theory  and  construction  of  tele- 
scopes,  or  how  they  are  put  together,  or  the  names  of  the 
different  sorts  of  lenses  which  he  uses  each  time  that  he 
handles  his  telescope.  In  mentioning  the  range  of  astronomy 
it  must  not  be  forgotten  how  important  to  us  all  (at  times)  is 
that  branch  or  subdivision  of  the  subject  which  goes  by  the 
name  of  Nautical  Astronomy— the  application  of  the  science  to 
the  navigation  of  ships  ;  but  that,  of  course,  is  entirely  beyond 
the  scope  of  this  work. 

I  hope  that  the  foregoing  ideas  will  be  realised  by  those 
people  who  read  this  book,  and  that  accordingly  they  will 
also  realise  the  fact  that  they  can  obtain  a  great  deal  of 
pleasure  and  profit  from  a  study  of  such  departments  of  as- 
tronomy as  may  be  readily  reached  without  great  exertions 
of  the  mind,  and  without  any  large  expenditure  in  the  way  of 
apparatus. 

There  is  only  one  more  subject  which  must  in  brief  form  find 
a  place  in  this  volume,  and  that  is  Spectroscopy.  It  is  only 
within  50  years  or  so  that  the  spectroscope  has  been  brought 
into  general  use  as  an  accessory  to  the  study  of  astronomy ; 
and  it  has  come,  almost  with  a  rush,  to  occupy  a  prominent 
place  in  the  minds  and  work  of  those  who,  going  beyond  the 
modest  aims  of  this  volume,  desire  to  dive  into  hidden  things 
which  do  not  in  the  first  instance  appeal  to  the  eyes  of  the 
casual  student  of  nature  who  takes  up  astronomy. 

In  order  not  to  burden  the  pages  of  the  book  with  uninviting 
masses  of  figures,  statistics  involving  numerical  quantities  will 
to  a  certain  extent  be  excluded  from  the  text  and  relegated 
to  an  Appendix,  where  they  will  be  more  accessible  for  consulta- 
tion and  comparison. 


CHAPTER    II. 
THE  SUN. 

Important  position  occupied  by  the  Sun. — Its  general  appearance. — Its 
mottled  surface- — ' '  Granulations  ' '  probably  the  best  word  to  describe 
it. — Spots  on  the  Sun. — Their  periodicity. — General  description  of 
them. — Peculiarities  of  spots. — Period  of  the  Sun's  rotation. — The, 
Photosphere. — Distribution  of  the  spots  in  latitude. — Discovery  of 
the  periodicity  of  the  spots. — Aurora. — Terrestrial  Magnetism. — 
Sun-spots  and  terrestrial  weather. — Possible  influence  of  some  of 
the  Planets  on  Sun-spots. — Wilson's  theory  respecting  them. — Vortex 
movements  on  the  Sun. — Faculce. — Apparent  movements  of  spots 
at  different  seasons  of  the  year. — Notable  large  spots. — Light-  and 
heat-giving  powers  of  the  Sun. — The  Krakatoa  sunsets. 

WE  are  so  accustomed  to  see  the  Sun  and  feel  its  heat-giving 
effects  that  we  are  apt  to  lose  sight  of  the  important  position 
which  it  occupies  in  the  Universe — or  perhaps  I  ought  rather 
to  say  in  our  Solar  System,  because  the  Universe,  in  the  proper 
sense  of  the  term,  extends  far  beyond  our  Solar  System,  which 
is  probably  only  one  of  many  systems,  and  perhaps  even  not 
the  most  important.  The  late  R.  A.  Proctor  entitled  one  of 
his  many  books,  "  The  Sun  :  Ruler,  Fire,  Light,  and  Life  of  the 
Planetary  System."  The  phrase  was  a  comprehensive  one,  but 
did  not  go  beyond  the  legitimate  expression  of  the  facts. 

Everybody,  I  suppose,  knows — at  any  rate,  in  a  general 
way — that  the  Sun  is  the  centre  of  our  Solar  System,  not  only 
in  the  sense  in  which  the  nave  is  the  centre  of  a  carriage-wheel, 
but  as  the  immediate  and  the  prime  source  (humanly  speaking) 
of  all  light  and  life  on  the  Earth  ;  moreover,  it  is  also  the 
central  force  which  keeps  everything  going.  To  pursue  this 

5 


6  THE    SUN. 

thought  further  would  lead  me  into  a  disquisition  on  the  Law 
of  Gravitation  and  the  laws  generally  of  Celestial  Motions, 
which,  it  will  be  understood  from  the  previous  chapter,  would 
be  foreign  to  the  aims  of  this  volume. 

If  we  look  at  the  Sun  soon  after  sunrise  or  towards  sunset, 
or  through  a  fog,  or  through  a  smoked  or  dark-coloured  glass, 
what  do  we  see  ?  Apparently  a  luminous  disc,  which  for  our 
present  purpose  may  be  regarded  as  a  true  circle,  though,  when 
it  is  viewed  near  sunrise  or  sunset,  the  circular  outline  is 
slightly  distorted.  To  the  naked  eye  this  disc  appears  as  a 
flat  patch  of  yellowish  light,  possessed  of  great  inherent  bright- 
ness and  powerful  heat-distributing  properties. 

But  this  is  a  very  poor  description  of  what  the  Sun  really  is. 
The  astronomer,  by  means  of  his  instruments  and  calculations, 
determines  it  to  be  very  large  and  not  flat,  but  globular  or 
spherical — a  ball,  in  fact.  To  the  naked  eye  the  Sun  seems  to 
have  the  same  smooth  surface  and  yellowish  tint  all  over  ;  in 
a  telescope,  however,  matters  are  far  otherwise.  The  surface 
appears  speckled  or  stippled,  and  near  the  limbs  or  edge  of  the 
circle  streaked,  whilst  every  now  and  again  and  here  and  there 
blackish  spots  are  sometimes  visible,  the  centre  of  the  Sun 
being  always  brighter  than  the  edges.  This  latter  fact  is  a 
very  obvious  result  of  its  globular  form,  but  the  mottling  and 
streaks  and  spots  depend  on  certain  physical  causes  which  are 
not  in  every  respect  capable  of  full  explanation. 

A  great  many  words  and  phrases  have  been  brought  into 
use  with  the  object  of  conveying  an  intelligible  idea  of  the 
appearance  of  the  surface  of  the  Sun.  "Willow-leaves,"  "rice- 
grains,"  "shingle  beach,"  "mottling,"  "stippling,"  "granula- 
tions," and  "  photospheric  network "  are  amongst  the  terms 
which  have  been  employed,  first  by  one  and  then  by  another 
observer.  The  last-named  term  is  decidedly  objectionable, 
because  it  conveys  too  much  the  idea  of  an  artificial  formation. 
On  the  whole,  because  of  its  vagueness,  I  am  inclined  to  prefer 
the  word  "granulations"  as  being  most  expressive  of  the 


THE    SUN'S    SURFACE.  7 

ordinary  appearance  of  the  Sun  in  telescopes  of  sufficient  .size 
to  show  anything. 

A  great  controversy  raged  over  several  of  these  phrases  half 
a  century  or  less  ago.  The  term  "willow-leaf"  was  put  for- 
ward by  Mr.  James  Nasrnyth,the  inventor  of  the  steam-hammer, 
who  in  his  later  years  became  a  great  observer,  being  also  very 
skilful  with  his  pencil.  His  idea  was  that  the  whole  surface  of 
the  Sun  exhibited  the  appearance  which  would  be  presented  by 
a  large  mass  of  willow-leaves  if  flattened  out  and  lying  pro- 
miscuously one  on  the  top  of  another  at  all  possible  angles. 
Though  the  term  "willow-leaf"  did  not  meet  with  general 
acceptance,  it  set  astronomers  thinking  how  they  could  best 
describe  the  general  appearance  of  the  Sun's  surface,  which  all 
agreed  was  not  smooth  and  uniform,  as  a  planed  slab  of  wood 
covered  with  a  coating  of  oil-paint  appears  smooth  and  uniform. 
Langley's  well-known  picture  of  what  he  called  a  "Typical 
Sun-spot"  brings  out  the  "willow-leaf"  idea,  though  I  do  not 
think  he  used  the  words.  [Plate  II.] 

Sir  W.  Huggins,  one  of  our  greatest  and  most  experienced 
English  observers,  took  up  the  subject  very  carefully  at  the 
time,  and  summarised  his  conclusions  by  giving  the  preference 
to  the  word  "granule,"  because  no  positive  form  is  implied  by 
its  use.  He  thought  "rice-grain"  was  a  suitable  expression  to 
represent  what  was  seen  in  small  telescopes,  but  that  there  was 
thereby  implied  a  definiteness  of  shape  which  to  some  extent 
disappeared  when  large  telescopes  and  high  powers  were 
resorted  to.  He  thought,  however,  that  it  might  safely  be  said 
that  these  objects,  whatever  their  nature,  did  affect  an  elongated, 
oval,  or  lenticular  form. 

These  opinions  have  not  been  seriously  disturbed  by  later 
discoveries,  and,  on  the  whole,  it  may  be  said  that  the  general 
surface  of  the  Sun  presents  a  granulated  appearance  to  which 
some  apply  the  word  "  network,"  though,  as  I  have  said  before, 
I  think  the  word  is  too  precise.  Another  word  in  use  is  "  pore  "  ; 
and  this  has  something  to  recommend  it,  because  when  the 


8 


THE    SUN. 


spots  (presently  to  be  described)  break  out,  they  often  start 
from  a  pore  as  a  place  of  origin. 

Other  similes  have  been  suggested  for  the  granulations  on 
the  surface  of  the  Sun.  An  American  astronomer  has  likened 
them  to  the  snow-white  ends  of  coral.  He  says  that  the  picture 


Fig.  2.— Madrepora  Specifera. 

An  East  Indian  Variety  of  Coral. 

here  given  (Fig.  2)  of  a  specimen  of  East  Indian  coral  in  the 
Natural  History  Museum  at  Williams  College,  Massachusetts, 
"  held  at  arm's  length,  and  viewed  with  eyes  partially  closed, 
gives  a  tolerable  idea,  though  on  an  enlarged  scale,  of  the 
appearance  of  the  solar  mottling  as  seen  in  the  largest 
telescopes." 


GROWTH    OF   SUN-SPOTS.  9 

The  spots  on  the  Sun  are  a  very  notable  feature,  and  now 
and  again  become  a  very  striking  feature  visually,  and  the 
whole  history  of  their  observation  is  one  of  intense  interest. 
Before  the  invention  of  the  telescope  little  or  nothing  was 
thought  or  known  of  them,  because  it  was  only  at  long  intervals 
that  a  spot  sufficiently  large  to  be  seen  with  the  naked  eye 
became  visible.  And .  even  when  telescopes  did  come  into 
use,  and  spots  were  much  more  often  noticed,  it  was  a  long 
time — more  than  200  years — before  observation  of  them  came 
to  be  made  systematically,  and  some  250  years  before  it  was 
realised  that  their  visibility  from  time  to  time  depended  upon 
a  recognisable  law  of  periodicity. 

Before  dealing  with  this  law  let  us  consider  for  a  while  some- 
thing about  a  spot  on  the  Sun  qua  spot.  We  will  suppose  that 
on  a  certain  day  an  observer  turns  his  telescope,  armed  with 
a  suitable  dark  glass,  on  to  the  Sun,  and  that  he  notices  nothing 
but  the  uniform  granulated  surface  of  which  I  have  already 
spoken,  and  that  on  the  following  day  he  detects  a  little 
blackish  point.  If  he  watches  this  point  during  several  days 
he  will  notice  that  it  increases  in  size,  and  very  likely  develops 
into  two  blackish  points.  In  such  case  the  two  will  separate 
from  one  another  more  and  more,  become  larger  in  size  and 
probably  more  irregular  in  shape,  whilst,  when  they  have 
become  considerably  separated,  other  outbursts  will  take  place 
in  between  the  two  original  spots,  so  that  a  very  broken  but 
somewhat  regular  irregular  group  or  chain  of  spots  will  have 
sprung  up.  The  forward  spot  of  the  original  pair  will  become 
as  it  were  the  leader  of  the  group,  the  word  "  forward  "  being 
used  to  indicate  the  spot  which  is  at  the  end  of  the  group 
reckoning  in  the  direction  in  which  it  will  have  been  noticed 
that  the  group  is  moving  over  the  Sun's  disc,  which  will  be 
from  E.  to  W. 

It  is  necessary  to  give  an  explanation  here.  Whether  a  spot 
is  endowed  with  an  absolute  motion  of  its  own  is  an  inde- 
pendent question  which  may,  or  perhaps  may  not,  have  to  be 


10  THE   SUN. 

answered  in  the  affirmative  in  any  given  case  ;  but,  inasmuch 
as  the  Sun  is  endued  with  a  motion  of  rotation  on  its  axis, 
every  spot,  whatever  its  inherent  permanency  may  be,  will 
be  visually  noticed  to  be  constantly  in  motion  across  the 
Sun's  disc. 

As  the  Sun  rotates  on  its  axis  from  E.  to  VV.  in  about 
25^  days,  no  spot  can  remain  continuously  on  view  for  more 
than  about  half  of  this  period — actually  about  13  days — for  a 
reason  to  be  presently  given. 

If,  as  often  happens,  a  spot  has  a  lifetime  of  several  weeks, 
it  will,  after  disappearing  on  one  edge  of  the  Sun,  reappear  a 
fortnight  later  on  the  other  edge,  and  so  on  and  so  on,  it  may 
be  for  two  or  three  months  or  more. 

Let  us  now  go  back  to  the  chain  or  group  of  spots  with 
the  consideration  of  which  we  started.  This  will  be  seen  to 
undergo  incessant  changes — the  constituent  spots  increasing 
in  size  and  number  or  decreasing  as  the  case  may  be.  Sooner 
or  later  they  will  all  disappear,  being  smothered  or  blotted  out 
by  the  onward  rush  of  the  waves  of  luminous  matter  which 
constitute  the  ordinary  surface  of  the  Sun  as  seen  by  us,  and 
to  which  the  name  of  Photosphere  (or  shell  of  light)  has  been 
given. 

Spots  on  the  Sun  do  not  always  appear  in  groups  or  with  a 
gregarious  tendency,  for  sometimes  we  may  see  a  single  spot 
which  apparently  has  no  neighbours  or  belongings.  Near 
such  a  spot  sometimes  small  neighbours  may  spring  up,  or, 
on  the  other  hand,  it  may  retain  its  individuality  for  some  time, 
increasing  in  size  or  diminishing,  but  retaining  during  its  whole 
existence  a  compact  and  somewhat  symmetrical  form  which 
more  or  less  approximates  to  a  circle,  like  a  hole  bored  in  a 
piece  of  wood  by  a  gimlet,  which,  when  removed,  shows  the 
edges  to  be  rough  and  frayed. 

So  much  for  the  personal  appearance  of  an  average  Sun-spot, 
but  a  good  deal  remains  to  be  said  on  the  subject.  When  a 
spot  is  beginning  to  disappear  it  does  not  always  do  so  by 


CHANGES    IN    SUN-SPOTS.  IT 

a  uniform  contraction  all  round  its  circumference.  Not  un- 
frequently  the  final  closing  up  will  be  preceded  by  a  bridge 
of  luminous  matter  darting  over-  the  dark  area,  and  forming 
for  the  time  it  endures  a  bridge  over  the  dark  area,  making 
indeed  the  whole  appearance  to  be  that  of  two  small  spots  side 
by  side  instead  of  one  large  spot. 

The  mass  of  material  which  is  available  for  an  account  of 


3' 


Fig.  3.— Spot  on  the  Sun,  Aug.  14,  1868. 

the  Sun,  even  if  only  limited  to  the  standpoint  of  visual  obser- 
vation, is  so  great  that  it  is  very  difficult  to  know  how  much 
to  include  and  what  to  exclude  in  writing  an  account  of  the 
Sun.  Something  more,  however,  needs  to  be  said  as  to  the 
physical  appearance  of  the  Sun's  surface  and  of  individual  spots. 
We  talk  about  spots  on  the  Sun,  and  colloquially  call  them 
dark  spots  ;  but  that  adjective  is  really  only  a  relative  term, 
and  must  not  be  pushed  too  far.  The  ordinary  dark  central 


12  THE   SUN. 

part  of  a  spot  is  commonly  called  the  Umbra  (Lat.  "  shadow  "). 
This  is  surrounded  usually  by  a  fringe  of  a  lighter  shade  to 
which  the  name  of  Penumbra  is  applied  (Lat.  pene,  almost ; 
umbra,  a  shadow). 

These  two  portions  of  an  ordinary  spot  are  generally  very 
distinctly  defined,  and  the  umbra  does  "not  usually  pass  into 
the  penumbra  by  a  gradual  change  of  intensity.  It  occasion- 
ally happens  that,  within  the  limits  of  the  Umbra,  there  may 
be  noticed  a  small  patch  of  deeper  blackness  to  which  Dawes 
applied  the  term  Nucleus.  But  Dawes's  description  of  an 
ordinary  nucleus  as  "intensely  black"  is  again  a  misnomer, 
for  it  is  only  relatively  dark,  showing  in  reality,  according  to 
Langley,  a  violet  purple  hue.  One  spot  may  either  have  its 
own  penumbra,  or  several  spots  may  be  included  in  one 
penumbra.  Moreover,  the  outer  edges  of  a  penumbra  will 
usually  appear  darker  than  the  interior  portions.  This,  no 
doubt,  is  a  mere  effect  of  contrast.  The  outer  edge  of  a 
penumbra  is  generally  of  a  very  irregular  outline,  but  not 
always  so,  for  sometimes  the  outline  bears  a  certain  general 
resemblance  to  the  spot  which  it  surrounds.  Whilst  the 
spots  themselves  are  often  very  irregular  in  shape,  yet,  on 
the  other  hand,  they  are  sometimes  very  compact  and 
symmetrical — a  remark  still  more  true  of  nuclei  where  a 
nucleus  exists. 

The  duration  of  the  existence  of  a  spot  is  a  matter  of 
extreme  uncertainty.  Sometimes  a  spot  may  be  seen  to 
appear  and  disappear  in  the  course  of  a  few  hours  ;  or  it 
may  remain  visible,  disappearing  and  reappearing  several 
times  by  virtue  of  the  Sun's  axial  rotation,  as  already  pointed 
out.  It  cannot  be  said  that  every  spot  remains  absolutely 
fixed  in  its  position  during  the  period  of  its  visibility.  Some 
spots  certainly  have  a  motion  of  translation  of  their  own  which 
makes  it  impossible  to,  rely  upon  their  disappearance  and 
reappearance  as  a  means  of  deducing  the  exact  period  of  the 
Sun's  rotation. 


FIG.  4 


PLATE    II. 


FIGS.  5-8 


PLATE  in. 


Oct.   22,   1905. 


July  31,  1906. 


Feb.  7,  1907.  May  6,  1907. 

Disc  of  the  Sun,  showing  Spots  (E.  W.  Barlow}. 


FIGS.  9-12 


PLATE    IV. 


July  15,  1907. 


May  4,  1908. 


Aug.  3,  1908.  Sept.  2,  1908. 

Disc  of  the  Sun,  showing  Spots  (E.  W.   Barlow}. 


FIGS.  13-15 


PLATE    V. 


The  Great  Sun-spot  of  1865  (Howlett). 


APPARENT   MOVEMENTS   OF   SUN-SPOTS.  13 

However,  as  the  result  of  multitudes  of  observations  by 
various  observers,  we  shall  probably  be  not  far  wrong  in 
putting  this  at  25  days  8  hours.  It  must  be  noted,  however, 
that  these  figures  are  not  a  measure  of  the  time  which  a  spot 
takes  to  disappear  and  reappear  and  disappear  again.  This 
occupies  27  days  7  hours,  being  longer  than  the  true  rotation 
once,  on  its  axis,  of  the  Sun  itself,  because  between  the  com- 
mencement of  an  observation  dating  from  the  disappearance 
of  a  spot  at  the  eastern  limb  and  its  arrival  at  the  same  point 
again,  the  Earth  has  moved  forwards,  and  the  Sun  has,  so  to 
speak,  to  turn  a  little  farther  than  one  revolution  in  order 
to  be  again  abreast  of  the  Earth. 

We  have  not  yet  exhausted  the  special  features  of  the  Solar 
Orb  as  made  manifest  even  to  the  casual  observer.  In  the 
first  place,  the  intensity  of  the  solar  light  is  greater  in  the 
centre  than  at  the  exterior  limits  of  the  disc.  This  is  a  natural 
consequence  of  the  obvious  fact  that,  in  looking  at  the  edges, 
we  are  looking  through  a  thicker  layer  of  the  outer  coating 
of  the  Sun  than  when  we  look  straight  at  it  in  the  middle 
of  the  disc.  It  remains  now  to  answer,  or  to  try  and 
answer,  the  questions,  "What  is  the  Sun?"  and  "How  is  it 
put  together?"  These  questions  are  difficult,  and  are  very 
much  mixed  up. 

To  say  that  the  Sun  is  not  a  solid  body  as  the  Earth  is,  and 
with  a  luminous  atmosphere  surrounding  it,  is  a  statement 
altogether  inadequate,  and  beside  the  mark.  The  general 
opinion  now  is  that  there  is  probably  nothing  solid  in  the 
Sun,  but  that  it  is  an  enormous  mass  of  gaseous  matter  of 
various  kinds,  surrounding  which  are  two  or  more  shells  or 
strata  of  matter  of  different  chemical  constitution,  including 
hydrogen  gas,  and  divers  metallic  vapours.  To  the  innermost 
of  these  layers  the  name  of  Photosphere  has  been  given,  and 
this  is  the  visible  source  of  the  ordinary  solar  light  which 
reaches  the  Earth.  Next  outwards  comes  the  Chromo- 
sphere, a  thin  casing  of  luminous  matter,  chiefly  hydrogen 


14  THE   SUN. 

gas,  and  the  seat  of  the  Red  Flames  seen  in  total  eclipses  of 
the  Sun  ;  whilst,  still  reckoning  outwards,  there  is  a  third  shell 
to  which  the  name  of  "  Corona  "  has  been  given.  We  shall  have 
to  consider  further  some  of  these  matters  in  the  chapter  (post) 
which  treats  of  eclipses  of  the  Sun. 

The  spots  do  not  appear  promiscuously  all  over  the  Sun. 
They  are  never  seen  at  either  of  the  poles  or  anywhere  near 
them.  They  seldom  reach  a  greater  latitude,  N.  or  S.,  of 
the  Solar  Equator  than  about  30°  to  37°  ;  but,  even  within 
these  equatorial  regions,  they  are  not  promiscuously  distri- 
buted—that is  to  say,  they  are  rare  at  or  near  the  Solar  Equator, 
and  perhaps  may  be  said  to  be  most  usually  seen  in  latitudes 
between  10°  and  20°  N.  or  S.,  being  as  a  rule  more  numerous 
and  of  greater  general  size  in  the  northern  hemisphere, 
especially  between  the  latitudes  of  11°  to  15°.  I  shall  have  to 
recur  to  this  question  of  the  distribution  of  the  spots  in  latitude 
after  I  have  spoken  of  their  periodicity. 

This  is  a  very  interesting  and  important  detail.  For  more 
than  two  hundred  years  after  the  invention  of  the  telescope 
and  of  its  employment  in  the  observation  of  Sun-spots,  they 
were  regarded  as  haphazard  manifestations  of  some  kind  of 
outbursts  on  the  Sun's  surface,  the  causes  of  which  were  quite 
unknown,  and  least  of  all  were  imagined  to  be  subject  to 
any  laws. 

in  1826  a  German  amateur  named  Schwabe,  who  lived 
at  Dessau,  commenced  a  systematic  observation  of  the  Sun 
day  after  day.  He  appears  to  have  been  able  to  see  it,  on 
an  average,  about  300  days  in  every  year,  and  he  carried 
on  such  observations  for  about  30  years,  when  he  reached 
a  remarkable  stage  in  his  career.  He  seems  to  have 
begun  by  suspecting  that,  if  he  observed  the  Sun  through  a 
sufficiently  long  number  of  years,  he  would  find  that  the  spots 
were  subject  to  a  law  or  laws  of  some  sort.  Twelve  years 
enabled  him  to  satisfy  himself  that  there  was  a  periodicity 
about  them  :  he  then  spent  another  6  years  in  trying  to 


FIGS.   16-18 


PLATE  VI. 


Sun-spots. 

(i)  Oct.  20,  1905.     (2)  Nov.  16,  1905,  showing  granulations  and  faculce  (Barlow). 
(3)  June  22,  1889  (McK.). 


FIGS.   19-26 


PLATE    VII. 


.-r 


«! 

•^-*.A''' 


~_ 

'•m 


Sun-spots  in  1882  at  Various  Dates  (Corlie). 


PERIODICITY    OF    SUN-SPOTS.  15 

impress  astronomers  with  the  truth  of  his  opinion,  and  in 
the  course  of  another  period  of  12  years  or  more  he  was 
able  to  convince  mankind  that  the  periodicity  of  the  Sun-spots 
was  absolutely  assured  ;  and,  to  cut  a  long  and  very  inter- 
esting story  short,  it  will  suffice  for  me  now  to  say  that,  as 
regards  their  numbers,  the  spots  are  subject  to  a  period  of 
slightly  over  n  years.  Or,  to  put  it  in  another  way,  1911 
having  been  a  year  of  practically  no  spots  at  all,  1912  has 
seen  a  few  ;  they  will  now  go  on  increasing  every  year  until 
about  1916,  when  they  will  be  very  abundant,  reaching  their 
period  of  maximum  ;  they  will  then  diminish  until  1922  or  1923, 
when  very  few,  and  during  many  months  none  at  all,  will  be 
visible. 

This  question  of  periodicity  and  its  amount  of  in  years 
is  now  established  to  a  dead  certainty.  It  must  be  stated, 
however,  that  a  minimum  does  not  occur  midway  between 
two  maxima,  but  that  6J  years  elapse  between  a  maximum  and 
the  next  minimum,  leaving  4^  years  as  the  interval  between 
a  minimum  and  the  next  maximum.  These  precise  figures 
for  the  intervals  are  not,  however,  quite  assured. 

We  are  not  yet  able  to  put  a  very  explicit  interpretation 
upon  this  1 1 -year  period,  though  there  are  some  incidental 
coincidences  connected  with  it  which  are  striking  and"  unmis- 
takable. These  include  the  diurnal  variation  of  the  magnetic 
needle  and  manifestations  of  the  Aurora  Borealis.  It  is  beyond 
the  scope  of  this  volume  to  discuss  in  detail  terrestrial  magnet- 
ism and  the  Aurora.  It  must  suffice,  therefore,  for  me  to 
state  that  the  magnetic  needle  is  subject  to  a  minute  change 
of  an  oscillatory  character  in  the  nature  of  an  effort  on  the 
part  of  the  needle  to  turn  towards  the  Sun.  These  diurnal 
vibrations  are  not  uniform,  but  vary  in  extent  during  a  period 
of  years  now  recognised  as  being  about  1 1  years.  Mani- 
festations of  the  Aurora  also  vary  from  year  to  year  during 
1 1  years ;  and  now  comes  the  singular  coincidence  that 
maxima  of  terrestrial  magnetic  displays  and  of  auroral 


16  THE    SUN. 

manifestations  are  synchronous  with  maxima  of  Sun-spots,  and 
minima  with  minima. 

The  coincidences  which  have  just  been  pointed  out  will  be  far 
more  easily  realised  by  an  inspection  of  the  annexed  diagram 
than  by  the  fullest  verbal  description.  The  rise  and  fall  of 
the  curves  in  the  diagram  indicate  in  each  case  both  the 
extent  of  the  changes  and  the  dates  thereof ;  and  the  most 
cursory  inspection  of  the  three  divisions  of  the  diagram  will 
show  at  once  the  coincidences  of  maxima  and  of  minima  and  of 
dates. 

With  these  facts  before  us  it  is  not  permissible  to  doubt  that 
there  is  some  intimate  connection  between  certain  events 
which  happen  on  the  Sun  and  certain  events  which  happen  on 
the  Earth.  What  the  nature  of  the  connection  may  be  cannot 
quite  definitely  be  stated,  but  that  electricity  is  concerned  in 
the  matter  in  some  way  or  other  seems  perfectly  certain. 
There  is,  indeed,  more  evidence  on  record  than  I  have  yet 
stated.  For  instance,  on  September  i,  1859,  tvvo  English 
observers  in  different  places  were  examining  a  fine  group  of 
Sun-spots,  and  suddenly,  at  11.18  a.m.,  two  patches  of  bright 
light  burst  forth  in  front  of  the  spots.  They  were  at  first 
thought  to  be  due  to  a  fracture  in  the  screen  attached  to  the 
object-glass  of  the  telescope  ;  but  such  was  not  the  case.  The 
patches  of  light  were  distinctly  on,  or  connected  with,  the  Sun 
itself.  They  remained  visible  for  about  five  minutes,  during 
which  time  they  moved  a  short  distance. 

A  remarkable  fact  has  now  to  be  added.  Simultaneously 
there  happened  a  great  disturbance  of  the  magnetic  instru- 
ments at  the  Kew  Observatory,  followed  16  hours  afterwards 
by  a  violent  magnetic  storm,  during  which  the  telegraphs  were 
interrupted  and  Auroras  appeared.  This  incident  does  not 
stand  alone,  for  on  several  more  recent  occasions  large 
Sun-spots  and  marked  disturbance  of  instruments  recording 
terrestrial  magnetism  have  been  noticed  as  contemporaneous 
events.  Probably  the  truth  is  enshrined  in  the  following 


SUN-SPOTS    AND    WEATHER    ON    THE    EARTH  I'J 

words   of  Mr.  H.  C.   Lewis,  an   assistant   at  the   Greenwich 
Observatory  : — 

"  The  theory  is  not  improbable  that  Sun-spots  are  the  result 
of  solar  electrical  or  magnetic  storms,  and  that  Auroras  are 
the  result  of  a  disturbed  electrical  condition  of  the  Earth 
caused  by  induction  from  the  Sun.  The  common  cause  for 
both  phenomena  is  probably  cosmical." 

Maunder  has  summed  up  the  situation,  as  regards  the  ques- 
tion of  solar  magnetism,  thus  :  — 

"  It  is  evident  that,  besides  sending  to  us  light  and  heat, 
the  Sun  sends  us  some  kind  of  influence  which  comes  only 
from  certain  portions  of  its  surface.  We  find  that  there  is  a 
tendency  for  magnetic  disturbances  to  take  place  when  a  Sun- 
spot  is  on  a  definite  portion  of  the  Sun's  disc." 

The  question  is  often  mooted  as  to  whether  any  connection 
can  be  traced  between  the  prevalence  or  absence  of  spots  and 
the  character  of  the  weather  on  the  Earth.  The  evidence  as 
to  this  is  exceedingly  contradictory,  and  great  names  are  to  be 
found  ranged  on  both  sides  of  the  controversy,  and  it  is  really 
impossible  to  present  any  trustworthy  definite  conclusions. 

The  matter  has  been  approached  from  two  somewhat  inde- 
pendent standpoints,  namely,  terrestrial  temperatures  as  dis- 
tinguished from  terrestrial  rainfall.  Perhaps  it  is  in  respect  of 
temperatures  that  the  evidence  is  more  contradictory  than  in 
the  matter  of  rainfall.  For  instance,  Wolf,  a  well-known  Swiss 
observer,  considered  that  he  had  found  decisive  evidence  "  that 
years  rich  in  solar  spots  are  in  general  drier  and  more  fruitful 
than  those  of  an  opposite  character,  while  the  latter  are  wetter 
and  stormier  than  the  former."  Another  Swiss  observer, 
Gautier,  discussing  62  sets  of  observations,  extending  over 
1 1  years  and  taken  at  various  places  in  Europe  and  America, 
arrived  at  exactly  the  opposite  conclusion.  Professor  C.  P. 
Smyth  considered  that  a  great  wave  of  heat  passes  over  the 

2 


l8  THE    SUN. 

Earth  every  11  years  and  a  fraction,  and  nearly  coincident 
with  the  beginning  of  the  increase  of  each  Sun-spot  cycle. 
A  German  observer,  Steen,  collecting  materials  obtained  during 
30  years  ending  with  1903,  considered  that  there  was  evidence 
that  the  maxima  and  minima  of  thunderstorms  occur  at  about 
the  periods  when  Sun-spots  are  at  their  maxima  and  minima 
respectively. 

Perhaps  it  may  be  added  with  safety,  though  I  shrink  from 
dogmatising  on  the  matter,  that  a  year  of  high  temperature  is 
coincident  with  an  absence  of  Sun-spots.  This  idea,  which 
was  put  forth  by  E.  J.  Stone  about  1870,  as  the  result  of  30 
years'  observations  at  the  Cape,  and  by  Abbe  as  the  result  of 
60  years'  observations  at  Munich,  certainly  found  a  confirma- 
tion in  the  long  prevalence  of  intense  heat  in  1911,  which  was 
a  year  of  unusual  deficiency  in  Sun-spots. 

The  question  has  been  seriously  mooted  as  to  whether  spots 
on  the  Sun  are  subject  to  any  further  cycle  than  the  ii'i  year 
cycle,  and  whether  planetary  influences  come  into  the  question. 
It  seems  that  an  affirmative  answer  must  be  given  on  both 
these  points.  Wolf  considered  that  the  activity  of  the  Sun,  as 
indicated  by  spots,  has  two  further  periods  of  55^  years  and 
166  years  respectively ;  the  former  period  being  made  up  of 
5  normal  cycles  and  the  latter  of  15  normal  cycles.  This  is  a 
matter  which  needs  and  deserves  further  investigation. 

The  following  table  of  dates  of  recent  Sun-spot  maxima  and 
minima  will  be  useful  for  reference  : — 

Maxima.  Minima. 

1860-1 

1867-2 
1870-6 

1878-9 
1884-0 

1890*2 
1894-0 

1901-9 
1906-4 

1911 


FIGS.  27-30 


PLATE   VIII. 


Jan.  31 


Feb.  i 


COM  PAR/JTI  v 


3jo°  32.0" 


GREAT     SPOT 


AT     S U N  '5     Lt Ki  8 


Jan.     5 


#  -  » 


Feb.; 


The  Great  Sun-spot  of  February  1905. 


181 


FIGS.  31-35 


PLATE    IX. 


Changes  in  Spots  as  they  approach  the  Sun's  Limb. 

(E.  W.  Barlow.} 

1906.  (i)  May  13  ;   (2)  May  14  ;    (3)  May  15;   (4)  May  16  ;    (5)  Mav  18. 


WHAT   ARE  TttE   SPOTS.  1<) 

As  regards  planetary  influences,  there  is  a  considerable 
amount  of  testimony  to  show  that  the  prevalence  of  Sun-spots 
depends  in  some  way  on  the  position  of  certain  of  the  Planets 
with  respect  to  the  Sun.  Wolf  thought  he  found  traces  of  an 
influence  exerted  by  Venus  in  the  course  of  its  annual  revolu- 
tion round  the  Sun,  and  Balfour  Stewart  thought  that  Mercury 
and  Jupiter  might  also  be  brought  in  as  exercising  some  effect. 
The  influence  of  Venus,  assuming  it  to  be  real,  implies  that 
the  planet  causes  spots  to  break  out  in  longitudes  of  the  Sun 
which  are  opposite  to  the  planet,  though,  supposing  a  spot  to 
have  been  started  by  Venus,  its  maximum  developement  does 
not  take  place  till,  by  the  Sun's  rotation  on  its  axis,  the  place 
of  origin  has  been  carried  farthest  away  from  Venus. 

In  spite  of  the  distinguished  names  which  are  attached  to 
some  of  these  surmises  as  regards  planetary  influence,  I  do  not 
feel  inclined  to  rely  very  much  upon  them  because  of  the 
obvious  liability  to  mistakes  being  made  in  the  inferences, 
owing  to  the  general  complexity  of  the  whole  subject  and  the 
difficulty  of  proving  connections  of  cause  and  effect. 

A  large  amount  of  attention  has  been  bestowed  on  the  Sun 
of  late  years  by  astronomers  generally  throughout  the  world, 
with  the  especial  object  of  determining,  if  possible,  what  are 
the  causes  of  Sun-spots,  and  what  are  the  physical  circum- 
stances which  may  be  supposed  to  govern  them.  Much  pro- 
gress has  been  made,  but,  nevertheless,  more  information  than 
we  at  present  possess  is  needed.  The  oldest  and  most 
attractive  theory  of  the  spots  is  that  associated  with  the  name 
of  a  certain  Professor  Wilson,  of  Glasgow,  as  modified  by 
Sir  W.  Herschel.  This  assumed  that  the  Sun  is  surrounded 
by  two  atmospheres,  arranged  somewhat  as  the  skins  of  an 
onion,  the  outer  one  being  luminous  (thence  termed  the  Photo- 
sphere, as  already  mentioned)  and  the  inner  one  non-luminous, 
and  that  the  spots  are  rents  or  apertures  in  these  two  skins 
through  which  we  see  revealed  the  solid  body  of  the  Sun  itself. 

Bearing  in  mind  that  it  is  now  the  received  opinion  that  the 


20  THE  SUN. 

Sun  is  not  a  solid  body,  it  must,  nevertheless,  be  confessed  that 
the  Wilson  theory  has  something  very  attractive  about  it,  in 
view  of  what  one  sees  when  a  Sun-spot  is  scrutinised  with  a 
telescope.  Suppose  we  find  a  spot  somewhat  symmetrical  in 
shape,  and  in  the  middle  of  the  Sun's  disc,  and  watch  its 
gradual  change  of  place  towards  the  edge  by  reason  of  the 
Sun's  axial  rotation.  It  will  be  seen  that  such  a  spot,  whilst  it 
of  course  undergoes  foreshortening,  in  accordance  with  the 
natural  law  of  foreshortening  when  a  globe  is  turning  on  its 
axis,  undergoes  foreshortening  on  the  side  nearest  the  limb 
which  the  spot  is  approaching ;  so  much  so  that  the  penumbra 
on  that  side  will  have  ceased  to  be  visible  whilst  a  certain 
amount  of  penumbra  exactly  opposite  still  remains  in  view.  A 
person  carefully  studying  the  career  of  a  particular  spot  can 
hardly  fail  to  be  impressed  with  the  feeling  that  his  eye  is 
resting  on  a  cavity  with  sunken  walls,  so  to  speak,  all  round 
it,  not  necessarily  perpendicular,  but  rather  in  the  form  of  a 
funnel. 

This  theory  of  the*  nature  of  a  Sun-spot  finds  confirmation  in 
the  fact  that  now  and  again  a  large  spot,  when  it  is  passing  out 
of  view  and  turning  the  corner  of  the  disc,  so  to  speak,  gener- 
ally appears  as  a  notch  in  the  outline  of  the  disc— a  fact  which 
distinctly  favours  the  idea  that  the  spots  are  depressions,  and 
condemns  the  idea  (held  by  some)  that  the  spots  are  elevations 
above  the  general  surface  of  the  Sun.  Spots  as  notches  have 
not  infrequently  been  recorded  by  observers  ;  a  notable  case 
occurs  in  a  photograph  taken  at  Dehra-Dun,  in  India,  in  1884. 

The  newest  idea  l  respecting  the  condition  of  the  Sun  is  that 
put  forth  in  America  by  Professor  Hale  (a  highly  skilled 
observer)  that  he  has  detected  signs  of  Vortices,  or  cyclonic 
action  of  a  magnetic  nature,  in  connection  with  the  visible 
surface  of  the  Sun.  Hale  has  investigated  the  subject  in 

1  I  am  not  at  all  sure  that  this  idea  ought  to  be  considered  "new,"  because 
I  have  in  my  possession  a  drawing  by  Hewlett  dated  May  n,  1863,  which  is 
actually  labelled  what  it  shows,  "  Interesting  Vorticose  Group." 


FACUL^E.  21 

a  very  exhaustive  fashion,  and  his  conclusions  have  met  with 
much  acceptance  ;  but  it  is  only  fair  to  add  that  signs  of 
cyclonic  action  on  the  Sun,  and  of  a  disposition  for  the  granu- 
lations to  take  up  sometimes  a  spiral  form,  were  obtained 
and  noted  many  years  before  Hale  went  to  work  by  observers 
as  early  as  Huggins  and  Secchi  in  the  'sixties  and  'seventies 
of  the  last  century.  This  branch  of  solar  study  is  a  highly 
delicate  and  intricate  one,  requiring  skilled  observers  and 
large  and  special  instruments,  and  therefore  is  a  subject 
somewhat  beyond  the  scope  of  this  volume. 

Before  passing  away  from  the  Sun  from  a  sight-seeing 
standpoint,  I  must  not  omit  a  few  words  about  solar  faculce^ 
These  are  streaks  of  light  frequently  to  be  noticed  in  the 
equatorial  regions  of  the  Sun,  and  near  either  limb,  and 
often  running  somewhat  in  a  N.  and  S.  direction.  They  are 
generally  of  no  particular  form,  though  perhaps  a  policeman's 
truncheon  is  not  a  very  far-fetched  simile  to  convey  an  idea  of 
their  shape.  Without  exactly  pretending  tosay  what  they  are  in 
constitution,  it  seems  at  least  certain  that 'they  are  elevations 
or  ridges  in  the  Photosphere,  possibly  even  detached  masses 
of  luminous  matter  floating  in  or  on  the  Photosphere.  It  would 
seem  that  they  have  some  sort  of  association  with  spots,  in 
so  far  that  they  are  often  to  be  found  just  outside  the  penumbra 
of  a  disappearing  spot,  or  even  occupying  the  place  where  a 
spot  has  actually  disappeared.  [Figs.  36-37,  Plate  X.] 

The  fact  that  the  position  of  the'Earth  with  reference  to  the 
Sun  at  different  seasons  of  the  year  varies,  and  that  the  Sun's 
axis  is  inclined  to  the  plane  of  the  Ecliptic,  has  this  result, 
namely,  that  a  spot  on  the  Sun,  if  attentively  followed  during 
the  fortnight  it  occupies  in  crossing  the  Sun's  disc,  will  be 
found  to  pursue  a  path  which  differs  with  the  season  of  the 
year.  In  June  and  December  a  spot  will  seem  to  follow  a 
straight  path  diagonally  upwards  in  the  former  case,  and 
diagonally  downwards  in  the  latter  case  ;  whilst  in  March 
1  Latin  factila,  a  torch. 


22  THE    SUN. 

and  September  the  apparent  path  will  be  curved — with  the 
convexity  in  the  former  case  towards  the  North  Pole  and 
with  the  convexity  in  the  latter  case  towards  the  South 
Pole. 

Astronomical  writers  of  popular  books  generally  try  to  excite 
their  readers  by  giving  a  wonderful  array  of  figures  supposed 
to  represent  the  dimensions  of  remarkable  Sun-spots.  I  am 
not  convinced  of  the  usefulness  of  such  statistics,  and  I  shall 
give  but  a  very  few.  It  may  be  taken  for  granted  that  no 
Sun-spots  are  fairly  visible  to  the  naked  eye  unless  they  have 
a  breadth  of  at  least  50,000  miles,  but  many  spots  of  greater 
size  than  this  are  on  record.  For  instance,  on  March  15,  1858, 
a  spot  was  visible  having  an  angular  breadth  of  4',  or  about 
108,000  miles. 

This  chapter  may  be  brought  to  a  close  with  a  few  statistics. 
The  distance  of  the  Sun  from  the  Earth,  or,  to  put  it  more 
consistently,  of  the  Earth  from  the  Sun,  may  be  taken  as 
averaging  92,000,000  miles,  which  varies  slightly  in  the  months 
of  January  and  July,  when,  owing  to  the  ellipticity  of  the 
Earth's  orbit  the  Earth  is  nearest  the  Sun  and  farthest  from 
the  Sun  respectively.  Why  we  in  England  (and  in  the  Northern 
Hemisphere  generally)  experience  colder  weather  in  January 
than  we  do  in  July,  though  we  are  nearer  the  Sun  in  January 
than  we  are  in  July,  perhaps  needs  a  word  of  explanation. 

The  explanation  is  exceedingly  simple.  The  meridian 
altitude  of  the  Sun  in  January  is  low,  and  its  rays  reach  us 
through  a  certain  thickness  of  atmosphere,  and  much  of  the 
heat  is  therefore  lost  ;  but  in  July  the  meridian  altitude  of 
the  Sun  is  very  considerably  higher,  and  its  rays  descend 
upon  England  and  the  Northern  Hemisphere  more  nearly 
perpendicularly,  and  therefore  more  directly,  and  through  a 
thinner  depth  of  atmosphere  to  absorb  them.  The  diameter 
of  the  Sun  is  about  32'  of  arc  (say  just  over  |°),  or  about 
860,000  miles.  The  Sun's  mass,  or  attractive  power,  is  332,000 
times  that  of  the  Earth,  and  about  750  times  that  of  all  the 


FIGS.  36-37 


PLATE  X. 


June  28,  1884. 


Nov.  28  1884. 

Faculae  on  the  Sun  (Cortie). 


FIG.  38 


PLATE    XI. 


[23 


HEAT-GIVING    POWER    OF    THE    SUN.  23 

planets  put  together.  The  density  of  the  Sun  is  about  i^  times 
that  of  water. 

These  figures  are  an  indication  of  the  comparative  lightness 
of  the  Sun  as  a  matter  of  weight.  Many  experiments  have 
been  made  to  arrive  at  an  idea  both  of  the  heat-giving  and 
of  the  light-giving  power  of  the  Sun.  The  conclusions  as 
to  this  are  very  apocryphal,  and  do  not  deserve  much  weight. 
For  instance,  it  has  been  stated  that  our  annual  share  of  the 
heat  would  melt  a  layer  of  ice  all  over  the  Earth  100  ft.  in 
thickness,  or  heat  an  ocean  of  fresh  water  60  ft.  deep  from 
freezing-point  to  boiling-point ;  whilst  the  direct  light  of  the 
Sun  has  been  supposed  to  be  equal  to  that  of  5563  wax  candles 
of  moderate  size  at  a  distance  of  one  foot  from  the  observer. 
Such  figures  as  these  seem  rather  to  savour  of  "  Alice  in 
Wonderland." 

Though  attempts  have  been  made  to  calculate  and  state  by 
figures  the  heat-giving  power  of  the  Sun,  it  must  be  obvious 
that  all  such  calculations  can  only  be,  if  not  quite  imaginary, 
yet  very  wild  and  indeterminate.  It  is,  however,  worth  while 
to  record  a  few  practical  consequences  of  the  power  of  the  Sun's 
rays  being  what  they  are.  For  instance,  in  constructing  the 
Breakwater  at  Plymouth,  the  men  working  in  diving-bells  at 
a  distance  of  30  ft.  below  the  surface  had  their  clothes  burnt 
by  coming  under  the  focus  of  the  convex  lenses  fixed  at  the 
top  of  the  bell  to  let  in  the  light. 

Some  years  ago  the  bedroom  curtains  in  the  house  of  a  friend 
of  mine  at  Bromley,  in  Kent,  were  set  on  fire  by  the  concentrated 
Sun's  rays  ;  and  I  once  read  in  a  book  of  military  history 
relating  to  Sir  R.  Abercrombie's  expedition  to  Egypt  in  1801 
that  the  Turks  captured  from  the  French  a  brass  gun  which 
had  been  fitted  up  so  that  every  day  at  12  noon  the  gun  was 
fired  by  the  sun  igniting  a  charge  of  powder  by  means  of  a 
burning-glass  (i.e.  a  double-convex  lens),  which  focussed  the 
Sun's  rays  on  the  touch-hole,  and  so  ignited  some  powder: 

It  would  not  be  possible,  nor  indeed  desirable,  in  my  limited 


24  THE    SUN. 

space  to  describe  in  any  detail  the  various  pictures  of  Sun-spots 
given  in  this  chapter,  but  the  one  dated  August  n,  1868,  will 
really  serve  to  describe  a  good  many  Sun-spot  pictures.  The 
wisp-like  structure  of  the  penumbra  will  be  readily  realised, 
whilst  on  the  southern  side  of  the  vast  depression  (for  the 
penumbra  is  a  depression  thousands  of  miles  deep)  there  will 
be  noticed,  closely  packed,  a  vast  crowd  of  rice-shaped  grains 
which  appear  to  be  flowing  up  to  and  over  the  edge  of  the 
centre.  The  picture  also  shows  a  long  straggling  line  and 
small  spots  trailing  after  the  principal  spot,  which,  as  has 
already  been  mentioned,  is  often  a  feature  of  a  prolonged 
and  extended  group  of  spots.  It  may  help  to  convey  an  idea 
of  the  magnitude  of  these  spot  apertures  in  the  Sun's  outer 
atmosphere  if  I  say  that  the  one  under  consideration  is 
sufficiently  spacious  for  the  Earth  to  be  dropped  into  it  with- 
out touching  the  penumbra  on  either  side. 

Figs.  19-26  represent  various  Sun-spots  at  various  dates  as 
observed  at  the  Stonyhurst  College  Observatory,  and  have 
been  kindly  placed  at  my  disposal  for  reproduction  in  this 
volume  by  the  Rev.  A.  L.  Cortie,  S.J.  The  4  pictures  dated 
April  1882  show  the  day-by-day  changes  in  a  spot  in  the  course 
of  a  week  or  less.  The  spot  dated  Nov.  17,  1882,  was 
accompanied  by  a  great  magnetic  storm  and  a  magnificent 
display  of  Aurora.  The  spots  dated  Sept.  29  and  Oct.  2 
and  Sept.  13  and  Sept.  15,  1883,  are  examples  of  spots  with 
double  penumbrae.  Fig.  37,  dated  June  28,  1884,  gives  the 
whole  disc  of  the  Sun  with  certain  spots  and  a  remarkable 
manifestation  of  faculas.  The  picture  dated  Nov.  28,  1884, 
shows  a  very  fine  group  of  faculas  on  the  E.  limb  of  the  Sun. 
The  whole-page  plate  [VIII.]  dated  February  1905  gives  the  life- 
history  of  what  became  a  great  spot  from  its  developement  from 
a  few  small  spots. 

Fig.  38  is  a  representation,  taken  from  a  photograph,  of  the 
red  sunsets  for  "  Red  Light ")  which  created  so  much  sensation 
in  the  autumn  and  winter  of  1883,  and  which  were  regarded  as 


KRAKATOA    SUN    EFFECTS.  25 

one  of  the  most  remarkable  solar-terrestrial  effects  of  modern 
times.  The  strange  feature  of  the  Red  Light  was  the  peculiar 
halo  which  it  caused  around  the  Sun  by  day,  and  its  long 
duration  after  sunset.  At  that  time,  and  during  the  early 
evening,  the  colour  was  usually  orange-red,  or  even  rose,  and 
it  stretched  far  up  towards  the  zenith  with  a  bright  spot  at  the 
highest  point.  There  was  also  a  bright  spot  and  coloured  arch 
in  the  E.,  opposite  the  point  of  sunset,  as  if  due  to  a  reflection 
of  the  western  display.  The  phenomenon  chang'ed  rapidly, 
arch  succeeding  arch  with  changing  colours  as  the  sun  sank 
lower  and  lower.  It  will  be  remembered  that  the  phenomenon 
was  by  common  consent  ascribed  to  volcanic  (Just  sent  forth 
from  an  active  volcano  on  the  island  of  Krakatoa,  near  Java 
and  it  was  supposed  that  the  dust  was  belched  forth  in  such 
enormous  quantities  that  it  was  carried  round  and  round  the 
World  by  the  Earth's  axial  rotation. 


CHAPTER  III. 
THE  MOON. 

Next  after  the  Sun  in  popular  interest. — How  soon  visible  after  being 
new. — Its  phases. — Its  movement  through  the  heavens.  —  General 
physical  aspects. — Its- mountains. — The  walled  plains. — The  rills. 
— Mountain  chains. — Isolated  peaks. — Signs  of  volcanic  action. 
— Resemblance  between  lunar  and  terrestrial  volcanoes.  —  Names 
applied  to  the  principal  mountains.  —  The  so-called  seas  on  the 
Moon. — General  appearance  of  a  crater. — Changes  in  their  appear- 
ance owing  to  the  Moon's  axial  rotation. — The  motions  of  the  Moon 
very  complex. — The  Librations. — The  Harvest  Moon. — The  Hunter's 
Moon. — Brightness  of  the  Moon  compared  with  the  Sun. — Supposed 
influence  of  the  Moon  on  the  weaiher. — Other  influences  ascribed 
to  the  Moon. — The  "  New  Moon  in  the  Old  Moon's  Arms." — In- 
fluence of  the  Moon  on  clouds. — Influence  of  Moonlight  on  human 
beings,  a  fallacy. — Some  statistics. 

NEXT  after  the  Sun  the  Moon  ranks  as  the  celestial  object  best 
known  to  the  inhabitants  of  the  Earth,  though  we  do  not, 
under  ordinary  circumstances,  see  it  every  day.  This  is 
owing  to  the  fact  that,  during  the  third  quarter  of  the  Moon's 
monthly  circuit  of  the  heavens,  it  only  shines  when  most  of 
us  are  in  bed.  Still,  it  is  there  for  those  who  choose  to  rise 
early,  or  take  rest  very  late,  in  order  to  see  it.  Indeed,  except 
for  a  certain  number  of  hours,  usually  considered  for  good 
eyes  to  be  about  30  before  or  after  it  is  "new,"  the  Moon 
is  visible,  weather  permitting,  throughout  the  whole  of  its 
monthly  journey  round  the  Earth  as  projected  on  the  sky. 

The  phases  of  the  Moon — that  is  to  say,  the  ever-changing 
outline  of  its  illuminated  portion — are   so  well  known  that  it 

26 


FIG.  39 


PLATE    XII. 


The  Moon, 


FIG.  40 


PLATE    XIII. 


The  Phases  of  the  Moon. 


f27 


THE  PHASES  OF  THE  MOON.  27 

seems  almost  too  commonplace  to  describe  them  in  detail  ;  but 
something  must  be  said  on  the  subject. 

Let  us  start  with  what  is  called  a  "  New"  Moon,  which  means 
that,  after  the  Moon  has  completed  one  revolution  round  the 
Earth  ending  with  its  being  lost  in  the  Sun's  rays,  then,  after  pass- 
ing a  particular  point  when  Earth,  Moon,  and  Sun  are  all  in  a 
straight  line,  it  emerges  from  the  Sun's  rays  in  the  western  sky  in 
the  evening.  Each  night  thenceforward  it  gets  farther  and  farther 
away  from  the  Sun,  and  day  by  day  becomes  more  easily  visible, 
until  on  or  about  the  7th  day  it  reaches  a  position  we  designate 
as  its  "  First  Quarter  "  (lucus  a  non  lucendo),  which  means  that 
half  of  the  whole  circle  of  its  disc  is  illuminated,  and  it  is  then 
on  the  meridian  at  about  6  p.m.  On  or  about  the  I4th  day, 
it  is  "  Full  Moon,"  when  the  whole  disc  is  illuminated  and 
we  see  a  complete  circular  area  of  light.  The  Moon  is  then 
on  the  meridian  at  midnight.  It  still  proceeds  in  its  easterly 
course,  and  the  next  important  stage  brings  it,  at  about  the 
2  ist  day,  to  its  Third,  or,  as  it  is  more  commonly  called,  its 
"  Last  Quarter.'3  It  is  then  on  the  meridian  at  about  6  a.m., 
and  may  be  noticed  in  the  W.,  shining  brightly  or  dimly 
(dependent  on  whether  the  season  of  the  year  is  winter  or  sum- 
mer) at  or  near  the  time  when  it  is  the  ordinary  breakfast-hour 
of  the  ordinary  Englishman.  Still  moving  in  the  same  easterly 
direction,  it  will  again  come  into  u  conjunction"  with  the  Sun 
on  or  about  the  28th  day  from  which  we  started ;  that  is  to 
say,  it  will  again  be  "  New  "  at  or  near  the  time  of  midday. 
During,  however,  speaking  roughly,  the  26th,  27th,  and  28th 
days  it  will  be  shining  in  broad  daylight,  and  therefore  more 
or  less  invisible,  except  that  a  good  eye  with  a  good  telescope 
should  be  able  to  see  it  up  to  within  about  30  hours  of  actual 
conjunction,  being  the  30  hours'  interval  already  mentioned 
in  a  previous  paragraph.  [Fig.  40,  Plate  XI II.] 

The  terms  "  New,"  "  First  Quarter,"  "  Full,"  "  Last  Quarter," 
which  have  been  made  use  of  above  are  rather  in  the  nature 
of  fancy  phrases,  though  everybody  uses  them,  and  they  are 


28  THE    MOON. 

fairly  well  understood  ;  but,  when  employed  in  connection  with 
the  weather,  are  altogether  illusory  and  meaningless. 

The  special  attractions  of  the  Moon  from  the  spectacular 
point  of  view  are  its  mountains  and  the  other  physical  features 
of  its  surface,  including  those  to  which  the  names  of  "  seas  " 
and  "  walled  plains  "  have  been  given.  There  are  also  certain 
clefts  or  rifts,  to  which  the  name  of  "rills"  has  been  attached, 
and  perhaps  we  should  not  be  far  wrong  in  regarding  these  as 
cracks  in  the  lunar  surface.  The  mountains,  however,  are  the 
special  features  of  our  satellite  to  deserve,  as  indeed  they 
receive,  the  particular  attention  of  the  ordinary  sightseer.  It 
may  be  said  that,  as  on  the  Earth,  so  on  the  Moon,  the  mountains 
are  of  two  types  :  chains  of  mountains  and  isolated  mountains. 
The  character  of  the  former  is  sufficiently  obvious  from  the 
name,  but  the  isolated  mountains  are  of  a  twofold  character — 
single  peaks,  and  crater  mountains,  of  which  we  have,  on  the 
Earth,  few  examples  except  certain  volcanoes.  Here  we  come 
upon  a  marked  difference  between  the  mountains  of  the  Earth 
and  the  mountains  of  the  Moon.  Craters  on  the  Earth  are 
the  exception,  and  very  few  in  number  ;  craters  on  the  Moon 
are  the  rule,  and  in  overwhelming  numbers.  Indeed,  this 
is  hardly  putting  the  matter  strong  enough,  because  nearly  the 
whole  surface  of  the  Moon  is  made  up  of  crater  formations. 
This  fact  is  especially  interesting,  because  it  makes  it  perfectly 
clear  that,  at  some  past  time,  the  whole  surface,  as  we  now  see 
it,  took  its  ultimate  shape  as  the  result  of  volcanic  action. 
If  anybody  has  any  doubt  about  this  the  doubt  must  assuredly 
be  removed  by  comparing,  say,  a  photograph  of  the  Peak  of 
Teneriffe  with  that  of  any  number  of  lunar  peaks  selected 
promiscuously. 

All  the  principal  lunar  mountains  have  received  names, 
chiefly  those  of  men  eminent  in  science,  both  ancient  and 
modern.  This  system  of  nomenclature  dates  from  the  I7th 
century  having  been  instituted  by  an  Italian  astronomer  named 
Riccioli. 


FIG.  41 


PLATE    XIV. 


*o^<*¥ 


28] 


The  Moon's  Surface  Modelled. 

By  James  Nasmyth,  1861. 


PLATE    XV. 


The  Lunar  Mountain  Copernicus  (W.  H.  Pickering,  photo). 


[20 


DESCRIPTION  OF  THE  MOON'S  SURFACE.  29 

In  more  recent  times  the  greater  number  of  the  important 
mountains  have  been  measured  to  ascertain  their  height 
above  the  general  level  of  the  Moon,  above  which  some  of 
them  rise  to  an  elevation  of  20,000  ft.  The  work  of 
measuring  these  heights  was  carried  out  on  a  large  scale 
more  than  half  a  century  ago  by  two  German  astronomers 
named  Beer  and  Madler,  the  value  of  whose  labours  has 
been  universally  recognised.  The  work  is  one  of  some 
difficulty  owing  to  the  lack  of  water  on  the  Moon,  but  it  is 
accomplished  by  taking  observations  under  special  circum- 
stances of  the  angular  dimensions  of  the  shadows  of  the 
mountains  whose  height  it  is  desired  to  ascertain. 

The  portions  of  the  Moon's  surface  to  which  the  name  of 
"seas"  has  been  applied  were  so  called  originally  from  their 
supposed  nature  ;  but  it  is  now  quite  certain  that  there  is  no 
water  on  the  Moon,  and  that  these  areas  are  in  the  nature 
of  vast  plains  like  the  Steppes  of  Asia  or  the  deserts  of  Africa. 

The  seas  have  received  very  fanciful  names,  but,  as  they  are 
commonly  referred  to  by  the  Latin  form  of  their  names,  the 
result  is  not  so  irritating  as  when  the  English  translation  is 
employed.  The  following  are  some  of  the  names :  Mare 
Humorum,  Mare  Imbrium,  Mare  Nectaris,  Mare  Serenitatis, 
Mare  Tranquillitatis,  and  so  on.  These  names,  if  one  does 
not  think  to  translate  them,  may  pass  muster  ;  but  how  vapid 
they  sound  in  their  English  forms :  the  Sea  of  Liquids,  the 
Sea  of  Showers,  the  Sea  of  the  Drink  of  the  Gods,  the  Sea  of 
Serenity,  the  Sea  of  Tranquillity — unworthy  of  exact  science  ! 

A  lunar  crater  usually  consists  of  a  sort  of  basin  with  a 
conical  elevation  rising  from  the  centre,  and  a  raised  rim 
encompassing  it.  The  cases  of  a  crater  mountain  not  having 
a  circular  contour  are  rare  ;  sometimes,  however,  a  crater 
may  be  thought  to  be  elliptical,  but  this  is  probably  in  most 
eases  a  perspective  effect  due  to  the  foreshortening  of  the 
crater,  which  will  be  one  seen  near  the  Moon's  limb. 

A  verbal  description  of  the  appearance  and  structure  of  one 


3O  THE   MOON. 

crater  would  more  or  less  serve  to  describe  every  crater,  and 
in  real  truth  no  verbal  description  is  worth  much  ;  the  craters 
must  be  seen  either  in  photographs,  or  in  drawings,  or  through 
a  telescope  for  the  features,  which  all  of  them  have  more  or 
less  in  common,  to  be  properly  realised. 

In  examining  the  craters  by  means  of  a  telescope  it  is  im- 
portant to  bear  in  mind  that  it  is  only  at  the  same  period  in 
each  lunation — that  is  to  say,  at  the  same  age  of  the  Moon  in 
days — that  a  crater  always  looks  the  same.  The  constant 
movement  of  the  Moon  round  the  Earth,  and  consequently 
the  constant  changes  in  the  amount  of  sunshine  falling  on  the 
Moon,  makes  the  mountains  present  an  incessantly  varying 
appearance.  In  the  case  of  mountains  situated  near,  but  just 
outside,  the  terminator  (as  the  line  dividing  the  illuminated  from 
the  un illuminated  portion  is  called)  the  changes  in  question 
may  often  strike  an  observer,  even  from  hour  to  hour.  The 
tips,  of  course,  of  the  mountains  may  be  in  sunshine,  whilst  the 
adjacent  valleys  are  in  shade ;  and  the  size  and  appearance 
of  the  tips  are  things  always  changing.  At  one  moment  two 
tips,  perhaps,  may  be  visible  as  bright  points,  whilst  after  a 
short  interval  a  third  will  become  visible  ;  or,  on  the  other 
hand,  the  two  tips  first  seen  may  become  invisible,  whilst  a 
new  intermediate  tip  may  come  into  view. 

At  or  near  the  epoch  of  Full  Moon  it  is  not  much  worth 
while  looking  at  the  Moon,  so  far  as  a  desire  to  examine  its 
formation  in  detail  is  concerned,  because,  the  Sun  then  shining 
straight  on  the  full  face  of  the  Moon,  there  will  be  no  shadows. 
On  this  account  the  Moon  can  best  be  studied  at  or  near  the 
Quarters,  or  when  the  Crescent  Moon  is  sufficiently  clear  of 
the  Sun.  At  such  times  the  shadows  cast  by  the  mountains 
will  fall  to  their  maximum  length  on  to  the  adjacent  valleys 
and  plains.  Be  it  remembered,  of  course,  that  they  will  point 
in  one  direction  when  the  Moon  is  waxing  and  in  the  contrary 
direction  when  it  is  waning.  . 

From  the  point   of  view  of  the    general   reader   who   only 


FIG.  -43 


PLATE    XVI. 


The  Mare  Crisium  on  the  Moon. 

From  a  Dr.uvine  bv  Professor  L.  Weinek  from  a  nesrativp  tn 


FIGS.  44-45 


PLATE    XVII. 


[31 


LI-BRATIONS    OF   THE    MOON.  31 

aspires  to  be  a  sightseer  there  is  not  very  much  more  to  say 
with  respect  to  the  Moon.  To  the  mathematical  astronomer 
the  Moon  has  given  a  great  deal  of  trouble  from  time  to  time 
because  its  motions  are  exceedingly  complex,  and  it  can  hardly 
be  said,  even  now,  that  the  subject  has  been  thoroughly 
mastered. 

Speaking  roughly,  we  may  say  that  the  same  hemisphere  of 
the  Moon  is  always  turned  towards  the  Earth  ;  but  this  is  not 
absolutely  true,  for,  owing  to  certain  physical  causes  connected 
with  the  position  of  the  Moon's  axis  with  respect  to  the  plane 
of  its  orbit,  and  the  inclination  of  that  plane  to  the  Ecliptic, 
the  poles  of  the  Moon's  axis  lean  alternately  to  and  from  the 
Earth.  Likewise,  the  Moon's  angular  velocity  in  its  orbit  is 
subject  to  a  slight  variation,  in  consequence  of  which  a  little 
more  of  its  eastern  or  western  edge  is  seen  at  one  time  than 
at  another. 

Moreover,  on  account  of  the  diurnal  rotation  of  the  Earth, 
we  view  the  Moon  under  somewhat  different  circumstances 
at  its  rising  and  at  its  setting  according  to  the  latitude  of  the 
place  on  the  Earth  at  which  we  make  our  observation. 

These  three  foregoing  sets  of  circumstances  give  rise  to 
three  irregularities  called  Librations,  respectively  known  as 
libration  in  latitude,  libration  in  longitude,  and  diurnal  libra- 
tion.  The  general  effect  of  these  librations  is  that,  comparing 
one  epoch  with  another,  we  see  a  narrow  strip  at  one  time 
which  we  do  not  see  at  another  time.  In  other  words,  though 
we  never  see  more  than  a  complete  hemisphere  at  one  time, 
yet  in  the  course  of  time  we  see  a  whole  hemisphere,  and  a 
little  bit  beyond,  all  the  way  round.  We  have,  in  fact,  a  sort 
of  surreptitious  look  round  the  corner. 

It  is  commonly  stated  that  the  Moon  possesses  no  atmo- 
sphere, and  this  is  in  substance  true  ;  but  very  refined  obser- 
vations of  planets  and  stars  when  occulted  by  the  Moon  suggest 
the  existence  of  an  atmosphere  so  infinitesimally  small  that 
W.  H.  Pickering  has  put  it  at  only  ^Vfrth  that  of  the  Earth. 


32  THE   MOON, 

He  says:  "Although  this  value  seems  small,  it  is  by  no  means 
insignificant,  and  would  correspond  to  a  pressure  of  hundreds 
of  tons  per  square  mile  of  the  lunar  surface." 

Two  expressions  connected  with  the  Moon  may  find  a  place 
here.  The  "  Harvest  Moon  "  and  the  "  Hunter's  Moon  "  are 
both  of  them  well-known  phrases — more  familiar,  however,  to 
dwellers  in  the  country  than  to  dwellers  in  towns.  The 
Harvest  Moon  is  that  Full  Moon  which  occurs  nearest  to 
the  autumnal  equinox.  As  the  Moon  then  rises  nearly  at  the 
same  hour  on  several  successive  evenings,  and  at  a  point  of 
the  horizon  almost  opposite  to  the  Sun,  the  duration  of  its 
visibility  at  night  is  about  the  maximum  possible.  The  pro- 
tracted moonlight  is  often  very  acceptable  to  the  farmer  at 
that  critical  period  in  his  agricultural  occupations. 

An  old  iSth-century  writer  on  astronomy  named  Ferguson 
thus  puts  the  matter: — 

"  The  farmers  gratefully  ascribe  the  early  rising  of  the  Full 
Moon  at  that  time  of  the  year  to  the  goodness  of  God,  not 
doubting  that  He  had  ordered  it  so  on  purpose  to  give  them  an 
immediate  supply  of  moonlight  after  sunset  for  their  greater 
conveniency  in  reaping  the  fruits  of  the  Earth." 

The  near  coincidence  in  several  successive  risings  of  the 
Moon  takes  place  in  every  lunation  whenever  our  satellite 
is  in  the  signs  Pisces  and  Aries ;  but  the  phenomenon  is  only 
prominently  noticeable  when  the  Moon  is  "full"  in  those 
signs,  and  this  only  occurs  at  or  near  the  autumnal  equinox 
with  the  Sun  in  Virgo  or  Libra.  The  Harvest  Moon  is  most 
useful  when  it  is  Full  Moon  about  September  23.  The  Moon 
may  then  rise  for  two  or  three  nights  in  succession  no  more 
than  10  minutes  later  each  night.  Under  different  circum- 
stances— that  is,  when  the  Moon  is  in  Libra,  and  at  or  near 
the  descending  node  of  its  orbit — it  may  rise  as  much  as  i£ 
hours  later  one  night  than  on  the  preceding  night. 

The  Full  Moon  next  following  the  Harvest  Moon  is  called 


LUNAR    EFFECTS.  33 

the  "  Hunter's  Moon,"  and  will  usually  fall  in  October.  There 
does  not  attach  to  it  the  same  glamour  that  attaches  to  the 
Harvest  Moon,  and  it  is  spoken  of  much  less  frequently.  It 
is  to  be  presumed  that  it  implies  that  the  operations  of  hunting 
will  commence  at  much  about  the  time  that  this  particular 
Moon  displays  itself  in  the  heavens. 

There  remains  to  be  mentioned  an  interesting  fact  in  con- 
nection with  the  light  afforded  by  the  Moon,  namely,  that  we 
in  the  Northern  Hemisphere  get  more  of  it  in  the  winter 
(when  it  is  most  wanted)  than  we  do  in  the  summer  (when 
we  can  most  readily  dispense  with  it).  These  differences  in 
the  availability  of  the  moonlight  are  due  to  the  fact  that  it  is 
in  the  winter  that  the  Moon  is  found  in  the  most  northern 
part  of  its  orbit,  because  the  Sun  at  the  same  time  is  exactly 
opposite  to  it  in  the  most  southern  part  of  its  (apparent)  orbit. 
The  nights  of  short  Moon  in  winter  are  also  the  nights  before 
and  after  the  New  Moon  when  there  is  the  least  possible 
amount  of  moonlight  to  lose. 

In  summer,  for  us  in  the  Earth's  Northern  Hemisphere,  the 
reverse  of  all  this  is  the  case  :  the  Moon's  elevation  above 
the  horizon  is  the  minimum  possible,  and  the  northern  hemi- 
sphere of  the  Earth  therefore  receives  the  minimum  amount  of 
moonlight. 

The  following  quotation  from  a  well-known  book  by  a  very 
well-known  man  brings  under  notice  the  Moon  in  quite  a  novel 
connection  : — 

"  The  evening  was  pleasant,  and  we  dined  in  the  open  air. 
All  the  valley  was  very  dark.  The  mountains  showed  a  velvet 
black.  Presently  the  moon  rose.  I  repress  the  inclination  to 
try  to  describe  the  beauty  of  the  scene,  as  the  valley  was  swiftly 
flooded  with  that  mysterious  light.  All  the  suitable  words 
have  probably  been  employed  many  times  by  numerous  writers 
and  skipped  by  countless  readers.  Indeed,  I  am  inclined  to 
think  that  these  elaborate  descriptions  convey  little  to  those 
who  have  not  seen,  and  are  unnecessary  to  those  who  have. 
Nature  will  not  be  admired  by  proxy.  In  times  of  war,  how- 

3 


34  THE   MOON. 

ever,  especially  of  frontier  war,  the  importance  of  the  moon  is 
brought  home  to  everybody.  '  What  time  does  it  rise  to-night?' 
is  the  question  that  recurs  ;  for  other  things — attacks,  '  sniping,' 
rushes — besides  the  tides,  are  influenced  by  its  movements."  1 

What  is  the  amount  of  the  light  sent  to  us  by  the  Moon? 
We  buy  and  sell  electric  lamps  calculated  to  display  so  much 
candle-power.  Can  we  make  any  analogous  calculation  with 
respect  to  the  light  of  the  Moon  compared  with  that  of  the 
Sun?  Such  calculations  have  been  made,  but,  as  was  to  be 
expected,  there  is  great  discrepancy.  More  than  a  century 
ago  Bouger  calculated  that  the  Moon's  light  was  only  TnnroTnrth 
that  of  the  Sun ;  several  more  modern  estimations  make  it 
much  less,  and  the  only  safe  conclusion  that  one  can  submit 
is,  that  if  the  whole  sky  was  covered  with  full  moons  we  should 
still  hardly  get  the  amount  of  daylight  which  we  owe  to  the 
Sun. 

The  question  of  the  Moon  influencing  the  weather  on  the 
Earth  has  already  been  alluded  to,  but  something  more  must 
be  said.  People  often  remark  in  common  conversation,  "  Ah  ! 
the  Moon  changes  to-morrow,  and  we  shall  have  a  change  of 
weather."  Supposing  that  on  the  aforesaid  to-morrow  the 
Moon  will  be  reaching  its  First  Quarter,  or  Eastern  Quadrature 
(to  use  the  proper  scientific  term),  the  exclamation  quoted  is 
intended  to  mean  that  directly  the  Moon  reaches  a  point  in 
its  orbit  90°  away  from  the  Sun,  whatever  has  been  the  weather 
during  the  few  days  before  the  Moon  reaches  that  point,  that 
weather  will  be  replaced  by  some  other  weather.  It  may  as 
well  be  stated  plainly  and  broadly  that  this  is  absolute  non- 
sense. I  will  here  quote  the  testimony  of  two  experts  on  this 
subject.  The  late  Astronomer  Royal,  Sir  W.  H.  Christie,  in  1896 
said  : — 

"  It  seems  doubtful  whether  the  Moon  has,  or  has  not,  any 
influence  on  the  weather  ;  but  it  is  clear  that,  in  any  case,  it  can 

'  W.  S.  CHURCHILL,  M.P.,  The  Malakand  Field  Foice,  18^7,  p.  174. 


FIGS.  46-51 


PLATE    XVIII. 


341 


FIGS.   52-57 


PLATE    XIX. 


[35 


WEATHER    NOT    AFFECTED    BY]THE    MOON.  35 

have  but  very  little  influence,  as  such  an  influence  has  never 
been  detected  with  certainty.  The  Moon's  place  is  always 
changing,  and  there  is  no  warrant  for  the  popular  idea  that 
the  instants  of  change  are  'new,'  'full,'  and  'first'  and  'last 
quarters.'" 

If  this  pronouncement  is  not  sufficiently  emphatic,  perhaps 
another  somewhat  similar  one,  taken  from  a  letter  from  the 
Meteorological  Office  in  London,  may  convince  a  Moon- 
believer  :  — 

"  No  one  in  his  senses  can  believe  in  the  Moon's  influence 
on  the  weather.  The  fact  that  storms  move  over  the  surface 
of  the  Earth  is  sufficient  to  show  that,  if  the  change  of  weather 
suits  the  Moon  in  Ireland,  it  must  fail  to  suit  it  in  England." 

It  is  very  remarkable  how  deeply  ingrained  in  the  minds  of 
people  is  the  idea  that  the  Moon  influences  the  weather,  and 
that  what  are  very  inappropriately  called  "  changes  of  the 
Moon"  bring  about,  or  are  associated  with  changes  in 
the  weather.  Most  grotesque  of  all  is  the  idea  that  it  makes 
a  difference  in  the  consequential  result  whether  a  so-called 
"change  of  the  Moon"  occurs  at  one  particular  hour  rather 
than  at  another.  In  real  truth  the  word  "  change "  in  this 
connection  is  a  curious  misnomer,  which  has  no  astronomical 
basis ;  and  neither  literally  nor  even  figuratively  has  the 
slightest  foundation  in  fact.  Perhaps  the  situation  may  be 
brought  home  to  some  by  asking,  Who  would  suggest  that  an 
express  train  travelling  from  London  to  Manchester  without 
stopping  at  Rugby,  and  returning  via  Oxford  without  stopping 
at  Birmingham,  underwent  a  "  change  "  when  it  passed  through 
Rugby  and  Birmingham  ? 

Notwithstanding  what  I  have  said  above,  there  are  a  few 
genuine  weather  signs  which,  it  may  be  admitted,  are  associated 
with  the  Moon,  but  have  no  physical  connection  with  it.  For 
instance,  if  the  Moon  looks  pale  and  the  horns  blunt,  or  lack 


36  THE   MOON. 

sharpness,  rain  is  indicated  ;  but  if  the  Moon  is  clear  and  sharp 
and  silvery  bright,  so  to  speak,  it  is  a  sign  of  fine  weather  which 
is  likely  to  continue.  An  old  adage  which  has  come  down  to 
us  in  Latin  from  I  know  not  what  date  runs  thus  : — "A  pale 
moon  indicates  rain  ;  a  red  moon  wind  ;  a  clear  moon  fair 
weather." 

It  often  happens  that  when  the  Moon  is  two  or  three  days 
old  the  dim  outline  ofthe  portion  not  directly  illuminated  by  the 
Sun  can  be  seen,  shining  with  a  pale  grey  light.  This  appear- 
ance is  popularly  called  "  the  New  Moon  in  the  Old  Moon's 
arms,"  though  it  would  be  better  to  put  it  the  other  way  about 
and  call  it  "  the  Old  Moon  in  the  New  Moon's  arms."  The 
appearance  may  be  taken  as  a  sign  of  rain,  being  the  equivalent 
of  the  clearness  of  distant  hills,  which  clearness  is  an  almost 
invariable  forerunner  of  rain.  It  is  sometimes  suggested  that 
the  question  of  the  effective  meaning  of  this  sign  depends  upon 
the  position  of  an  imaginary  line  joining  the  horns  relatively  to 
a  horizontal  or  an  inclined  position  ;  but  nothing  depends  on 
this,  because  the  position  as  regards  level  of  the  line  joining  the 
horns  is  simply  a  matter  which  depends  upon  the  season  of 
the  year  as  regards  the  place  of  the  Moon  in  the  heavens  with 
respect  to  the  Sun.  [Plate  XXII.] 

When  the  Moon  is  near  its  full,  either  before  or  after,  it  fre- 
quently happens  that,  as  the  Moon  rises  in  the  sky  on  a  cloudy 
night,  the  clouds  break  up  and  disperse  as  the  night  wears  on. 
I  regard  this  as  a  well-authenticated  fact,  which  I  observed 
myself  many  years  ago  before  I  knew  that  Sir  J.  Herschel  had 
also  put  it  in  print,  and  I  may  add  that  I  have  often  noticed  it 
myself  since,  though  Mr.  W.  Ellis,  late  of  the  Greenwich 
Observatory,  once  sought  to  controvert  it.  It  seems  to  confirm 
the  idea  that  the  Moon  imparts  a  certain  but  very  faint  amount 
of  warmth  to  the  Earth,  as  the  direct  observations  of  the  late 
Earl  of  Rosse  distinctly  indicate. 

Subject  to  the  foregoing  exceptions,  it  may  be  said  that  the 
following  composition  of  some  unknown  "poet  "  (save  the  mark !) 


FIGS.  58-63 


PLATE    XX 


36] 


FIGS.  64-67 


PLATE    XXI. 


Atlas  and  Hercules. 


The  Apennines. 


Alphonsus.  Aristarchus. 

Mountains  on  the  Moon  (Stuyvearf).  [P.  37 


POPULAR    DELUSIONS.  37 

correctly  represents  the  facts  as  regards    the    Moon  and  the 
weather  : 

"The  Moon  and  the  weather 
May  change  together, 
But  change  of  the  Moon 
Does  not  change  the  weather  ; 
If  we'd  no  Moon  at  all — 
And  that  may  seem  strange — 
We  still  should  have  weather 
That's  subject  to  change." 

Besides  the  question  of  terrestrial  weather,  the  Moon  is  credited 
with  other  influences,  some  genuine  ;  some  perhaps  genuine,  but 
more  likely  mythical.  The  most  genuine  lunar  influence  is  its 
effect  on  the  tides  of  the  ocean — a  subject  of  sufficient  im- 
portance to  demand  a  separate  chapter  hereafter.  The 
influence  which  I  have  described  as  perhaps  genuine  is  one 
which  is  wholly  independent  of  the  so-called  changes  of  the 
Moon.  It  is  that  perhaps  it  is  more  often  rainy  during 
the  increase  of  the  Moon  from  New  to  towards  Full 
than  from  Full  to  towards  New.  Moreover,  that  when 
the  Moon  is  in  perigee,  or  nearest  the  Earth,  the  chances  of 
rain  are  greater  than  when  it  is  in  apogee,  or  farthest  from 
the  Earth. 

Contrary  to  the  prejudices  of  most  people,  perhaps  one  might 
say  of  the  great  mass  of  mankind,  the  epoch  of  New  Moon  is 
the  period  when  changes  of  weather  may  be  least  looked  for. 
The  alleged  lunar  influences  which  must  be  regarded  as 
mythical  are  too  many  to  be  recited  here.  Perhaps  the  most 
prominent  is  that  which  is  enshrined  in  the  word  lunatic,  which 
philologically  may  be  taken  to  imply  that  the  Moon  has  some- 
thing to  do  with  people  going  out  of  their  minds  ;  but,  without 
going  so  far  as  this,  one  often  comes  across  passages  in  books 
the  writers  of  which  insinuate  that  the  rays  of  the  Moon  exercise 
a  mischievous  influence  on  human  beings  exposed  to  them. 
This  is  especially  an  idea  current  in  the  East,  though!  it  finds  a 


38  THE    MOON. 

counterpart  in  ideas  met  with  nearer  home.     A  writer  named 
Carne  has  remarked  : — 

"  The  effect  of  the  Moonlight  on  the  eyes  in  Eastern  Coun- 
tries is  singularly  injurious.  The  natives  tell  you  always  to 
cover  your  eyes  when  you  sleep  in  the  open  air  ;  indeed,  the 
sight  of  a  person  who  should  sleep  with  his  face  exposed  to  the 
Moon  at  night  would  soon  be  utterly  impaired  and  destroyed." 

Another  writer,  named  Anderson,  speaking  of  Batavia,  is  still 
more  thrilling  in  his  language  : — 

"  One  must  here  take  great  care  not  to  sleep  in  the  beams  of 
the  Moon  uncovered  ;  I  have  seen  many  persons  whose  necks 
have  become  crooked,  so  that  they  look  more  to  the  side  than 
forwards." 

A  writer  of  very  ancient  date,  Plutarch,  remarked  that  the 
light  of  the  Moon  causes  animal  substances  to  putrefy  ;  and  it 
is  said  that  Sicilian  fishermen  cover  during  the  night  fish  which 
they  expose  on  the  sea- shore  to  dry,  and  for  the  same  reason. 
Even  before  the  time  of  Plutarch,  Virgil,  when  describing  the 
descent  of  yEneas  into  Hades,  speaks  of  the  incertam  Lunam 
sub  luce  malignd,  "  the  Moon's  doubtful  and  malignant  light."  * 
The  old  forest  laws  of  France  forbade  the  felling  of  trees  except 
during  the  waning  of  the  Moon,  and  a  Scotch  writer,  many  years 
ago,  stated  that  peat  dug  during  the  increase  of  the  Moon 
continues  moist  and  never  burns  clear. 

The  writers  of  a  very  well-known  book 2  make  the  following 
statement  in  it : 

"  Lunar  influence  seems  to  occasion  phenomena  of  a  very 
curious  nature.  It  is  confidently  affirmed  that  it  is  not  unusual 
for  men  on  board  a  ship,  while  lying  in  the  moonlight,  with 

1  sEneid,  book  vi.  line  270.  I  borrow  from  Milner's  Astronomy  the 
translation  of  "malignant "  for  malignd ;  but  Valpy  renders  it  "  faint  and 
glimmering,"  which  wholly  changes  the  simile. 

"  Voyages  and  Travels  round  the  World,  by  the  Revf  D.  TYERMAN,  and 
G,  BENNETT, 


STATISTICS.  39 

their  faces  exposed  to  the  beams,  to  have  their  muscles  spas- 
modically distorted  and  their  mouths  drawn  awry — affections 
from  which  some  have  never  recovered.  Others  have  been  so 
injured  in  their  sight  as  to  lose  it  for  several  months.  Fish, 
when  taken  from  the  sea-water,  and  hung  up  in  the  light  of  the 
Moon  during  a  night,  have  acquired  such  deleterious  qualities 
that,  when  eaten  the  next  day,  the  infected  food  has  produced 
violent  sickness  and  excruciating  pains.  We  have  conversed 
with  people  who  have  been  themselves  disordered  after  having 
partaken  of  such  fish.  It  is  hazardous  to  touch  on  this  subject  ; 
we  repeat  what  we  have  heard  from  those  who  ought  to  be 
believed,  and  who  would  not  affirm  that  of  which  they  them- 
selves were  not  persuaded." 

There  is  a  circumstantial  element  of  good  faith  in  the  fore- 
going quotations,  which  makes  it  impossible  to  disbelieve  the 
facts  stated.  But  where  the  writers  have  gone  astray,  and 
others  have  gone  astray  with  them,  is  in  their  erroneous  explana- 
tion of  real  facts.  The  explanation  seems  to  be  this.  Animal 
substances  may  seem  to  putrefy,  and  peat  to  become  moist,  and 
human  beings  to  become  subject  to  bodily  ailments  when 
exposed  to  the  light  of  the  Moon,  not  because  of  that  light,  but 
because  owing  to  the  absence  of  clouds  (the  sky  therefore  being 
clear  to  permit  a  full  display  of  moonshine),  the  radiation  of  heat 
from  the  Earth's  surface  is  facilitated,  so  that  objects,  whether 
animate  or  inanimate,  become  colder  than  the  surrounding  air  ; 
the  deposition  of  dew  is  therefore  facilitated,  and  it  is  the 
moisture  thus  engendered  which  hastens  the  developement  of 
muscular  pains  and  bodily  ailments  in  animated  beings,  and 
decomposition  and  putridity  in  inanimate  objects. 

The  Moon  travels  round  the  Earth  in  27  days,  7  hours, 
43  minutes  at  a  mean  distance  of  237,300  miles.  Owing  to  the 
fact  that  its  orbit  is  not  a  circle  but  an  ellipse,  the  eccentricity 
of  which  is  0*05,  it  may  sometimes  be  as  near  to  the  Earth  as 
221,600  miles,  or  may  recede  to  as  far  as  253,000  miles.  In 
consequence  of  this  eccentricity  its  apparent  diameter  may  vary 
between  29'  21"  and  33'  31".  Its  diameter  at  mean  distance  is 


40  THE    MOON 

31' 5"  ar;d  its  true  diameter  is  about  2,160  miles.  It  will  be 
sufficiently  near  the  truth,  for  popular  purposes,  to  say  that  its 
diameter  as  we  see  it  is  about  ^°,  and  is  therefore  about  the 
same,  apparently  of  course,  as  that  of  the  Sun.  Owing  to  the 
influence  of  the  Earth's  atmosphere  the  apparent  diameter  will 
differ  somewhat  according  as  we  view  the  Moon  when  high 
up  in  the  sky  or  low  down  near  the  horizon. 


CHAPTER    IV. 
THE  TIDES. 

The  tides  matter  of  interest  to  the  inhabitants  of  maritime  countries. — 
Influence  of  the  Sun  and  Moon  in  causing  them, — Details  of  this 
influence. — That  of  the  Moon  greatly  preponderates. — Spring  Tides. — 
Neap  Tides. — Daily  differences. — Range  of  the  tide. — "  Establishment 
of  the  Port." — "Priming"  and  "lagging"  of  the  tides. — Equinoctial 
tides. — Tides  at  the  solstices. — Tidal  irregularities  of  various  kinds. 
— In  and  around  Great  Britain. — Amongst  the  South  Sea  Islands. — 
Influence  of  the  barometer. — Journey  of  the  tidal  wave  round  the 
Earth.— The  "Bore." 

THE  subject  of  the  Tides  of  the  Ocean  is  a  mixed  astronomi- 
cal and  geographical  one,  and  it  comes  so  much  home  to  the 
inhabitants  of  an  island  kingdom  such  as  Great  Britain  and 
Ireland  that  it  must  not  be  omitted  from  a  volume  which 
appeals  to  those  interested  in  studying  things  which  they  can 
see.  And  it  follows  naturally  chapters  devoted  to  the  Sun 
and  the  Moon,  because  those  two  luminaries  are  jointly  con- 
cerned in  causing  the  tides. 

Diagrams  illustrating  the  theory  of  the  tides  appear  in  every 
book  on  astronomy  and  need  not  appear  here  because,  as  it 
happens,  it  is  possible  to  explain  the  matter  without  diagrams, 
which  is  a  thing  not  always  possible  in  dealing  with  some 
scientific  problems. 

Let  us  take,  first  of  all,  the  case  of  the  Moon.  The  Moon  is 
the  Earth's  satellite,  and  as  such  is  primarily  responsible  for  the 
tides,  though,  as  we  shall  see  presently,  the  Sun  is  also  con- 
cerned in  a  lesser  degree. 

4* 


42  THE   TIDES. 

The  Moon,  being  the  Earth's  satellite,  is  in  a  sense  held  in 
its  place  by  the  attraction  of  the  Earth  ;  but  there  is  a  certain 
amount  of  mutuality  in  the  matter — that  is  to  say,  though  the 
Earth  attracts  the  Moon,  the  Moon  has  a  slight  attractive 
power  on  the  Earth,  but  it  does  not  suffice  to  do  much  more 
than  attract  the  water  on  the  Earth,  because  the  water  is 
mobile.  This  is  only  half  the  truth,  for  the  Moon  does  draw 
the  Earth  to  a  slight  extent ;  but  in  doing  so  the  water  on 
exactly  the  opposite  side  is  left  behind,  in  a  sense  heaped  up. 
Thus  it  comes  about  that,  whilst  it  is  high-water  when  the 
Moon  is  on,  or  near  the  meridian  of  the  place  of  observation, 
there  is  also  a  condition  of  high-water  on  the  opposite  side  of 
the  Earth  180°  removed  in  longitude  from  the  meridian  just 
spoken  of.  In  other  words,  the  coincident  tides  are  separated 
from  each  other  by  180°,  or  by  half  the  circumference  of  our 
globe.  Since  the  diurnal  rotation  of  the  Earth  on  its  axis 
thus  causes  the  tidal  waves  to  pass  successively  right  round 
the  Earth  once  in  about  every  24  hours  it  follows  that  as  there 
are  two  tidal  waves  constantly  in  motion,  there  are  everywhere 
two  high  tides  daily,  with  an  interval  of  about  12  hours 
between  them. 

Now  let  us  consider  the  influence  of  the  Sun  as  brought  into 
the  matter.  Though  the  mass  of  the  Sun  is  so  very  much 
greater  than  the  mass  of  the  Earth,  there  are  two  reasons  why 
the  power  of  the  Sun  to  raise  or  develope  tides  on  the  Earth 
is  much  less  than  its  preponderating  mass  would  lead  us  to 
suppose.  Firstly,  the  greater  distance  of  the  Sun  from  the 
Earth,  compared  with  the  distance  of  the  Moon  from  the  Earth, 
diminishes  the  power  of  the  Sun  compared  with  what  it  would 
be  were  the  distances  on  an  equality ;  and,  secondly,  the 
developement  of  the  tides  is  due  solely  to  the  inequality  of  the 
attractions  in  operation  on  different  sides  of  the  Earth,  so  that 
the  greater  the  inequality  the  greater  the  resulting  tide  and 
vice  versa.  The  mean  distance  of  the  Earth  from  the  Sun  is 
about  11,720  diameters  of  the  Earth,  and  consequently  the 


THE    THEORY    OF    THE    TIDES.  43 

difference  between  the  distance  of  the  Sun  from  one  side  of 
the  Earth  compared  with  the  other  will  be  only  Trhtfth  of  the 
whole  distance.  But  in  the  case  of  the  Moon,  whose  mean 
distance  is  only  30  diameters  of  the  Earth,  the  difference 
between  the  distance  from  one  side  compared  with  the  distance 
on  the  other  side  will  be  -sVth  of  the  whole  distance. 

Inasmuch,  therefore,  as  the  height  of  the  tidal  wave  depends 
on  the  inequality  of  the  attraction  and  the  inequality  being  in 
the  case  of  the  Moon  represented  by  A,  whilst  in  the  case 
of  the  Sun  it  is  only  TTTSTD  the  preponderance  of  the  influence 
of  one  of  these  two  bodies  over  the  other  is  obvious.  Worked 
out  mathematically  it  was  calculated  by  Newton  to  be  about 
2£  to  i. 

Thus  far  we  have  been  supposing  the  Sun  and  Moon  to 
be  pulling  together,  but  they  only  do  that  when  they  are  in  the 
same  straight  line,  which  is  when  the  Moon  is  what  we  call 
New  or  Full.  But  when  the  Moon  is  in  quadrature,  or  |th 
or  fths  of  the  way  round  in  its  orbit,  reckoned  from  the  stage 
known  as  New  or  Full,  then  Sun  and  Moon  do  not  pull  to- 
gether, and  the  resulting  tide  is  only  that  due  to  the  surplus 
influence  of  the  Moon  over  that  of  the  Sun  ;  in  other  words, 
the  resulting  tide  is  a  much  smaller  one  than  when  they  pull 
together.  This  explains  the  contrast  which  all  residents  on 
the  sea-coast  can  realise  between  the  high  and  low-water 
marks  which  they  observe  at  the  epochs  of  New  and  Full 
Moon  compared  with  the  rise  and  fall  of  the  tides  at  the 
Quarters.  The  former  tides  go  by  the  name  of  "spring 
tides,"  and  give  rise  to  the  highest  possible  and  lowest  possible 
high-water  and  low-water  marks  respectively.  The  latter  are 
known  as  "  neap  tides,"  and  result  in  only  a  moderately  high- 
water  mark  and  a  moderately  low-water  mark.  The  physical 
cause  of  these  last-named  circumstances  will  now  be  easily 
understood,  for,  whilst  Spring  Tides  depend  upon  Sun,  Moon, 
and  Earth  being  all  the  same  straight  line,  in  the  Neap  Tides 
the  Moon's  attraction  acts  along  a  line  perpendicular  to  that  of 


44  THE    TIDES. 

the  Sun  ;  in  other  words,  the  two  bodies  partly  neutralise  one 
another's  action. 

All  the  foregoing  remarks  have  been  based  on  the  assump- 
tion (which  is  baseless),  namely,  that  the  Earth  is  a  sphere 
covered  all  over  by  a  layer  of  water  of  uniform  depth  ;  but  it 
is  convenient  to  give  the  explanation  on  this  assumption  in 
order  to  make  the  matter  more  easily  intelligible,  and  for  this 
same  reason  the  following  propositions  are  framed  on  the 
same  supposition,  to  be  modified  by  subsequent  explanations. 

1.  On   the   day  of  New   Moon,    Sun   and    Moon  cross  the 
meridian  at  the  same  time,  namely,  at  noon  ;  then,  after  an 
interval,  high-water  occurs.     Then  the  water  begins  to  fall  for 
6  hours  12  minutes  till  it  reaches  its  lowest  position  ;  it  then 
rises  for  6  hours  12  minutes  to  a  second  maximum  ;  then  falls 
for  another  interval  of  6   hours   12  minutes,  and  rises   again 
during  a  fourth  interval  of  6  hours  12  minutes.     It  has,  there- 
fore,  two  maxima  and  two  minima  in  a  period  of  24  hours 
48  minutes,   which   is   called   a   "  tidal  day."     The   foregoing 
intervals  are  not  quite  correctly  expressed,  even  in  theory,  for 
the  water  usually  takes  a  longer  time  in  falling  than  it  does 
in  rising,  as  may  be   noticed  by  any  one  sitting   on  the  sea- 
shore. 

2.  On  the  day  of  Full  Moon  the  Moon  crosses  the  meridian 
12   hours   after,  the   Sun,   namely,  at  midnight,  and   the  tidal 
phenomena  are  the  same  as  stated  in  the  previous  paragraph. 

3.  As  time  is  reckoned  by  the  apparent  motion  of  the  Sun, 
the  solar  tide  always  happens  at  the  same  hour  l  at  the  same 
place  ;  but  the  lunar  tide,  which  is  the  greater,  and  therefore 
gives   a  character  to   the   whole,   happens   48   minutes   later 
every  day.     It  therefore  separates  eastwards  from  the   solar 
tide  at  that  rate,  and  becomes  later  and  later  till,  at  the  First 
and  Third  Quarters  of  the  Moon,  it  happens  at  the  same  time 

1  I  ignore  here  the  question  of  the  difference  between  apparent  solar  time 
and  mean  solar  time  and  the  customary  adjustment  of  these  times  by  what  is 
called  in  the  almanacks  the  "  equation  of  time." 


DETAILS   AS    TO   THE   TIDES.  45 

as  the  low-water  of  the  solar  tide  :  then  the  elevation  of  the 
high- water  and  the  depression  of  the  low  will  be  the  difference 
of  the  solar  and  lunar  tides,  and  the  condition  of  things  will  be 
represented  by  the  term  Neap  Tide. 

4.  The  difference  in  height  between  high  and  low-water  is 
called  the  "  range  of  the  tide,"  .and  obviously  may  be  measured 
in  two  ways  :  either  horizontally  along  the  shore  or  vertically  on 
a  post  of  suitable  height,  and  suitably  placed  for  the  purpose. 
The  former  principle  of  measurement  would  be  the  one  adopted 
by  an  unscientific  seaside  visitor,  but  the  latter  will  often  be 
noticed  as  measurable  by  numbered   marks  on   the  columns 
supporting  a  pier,  or  painted  on  the  upright  wall  of  a  jetty  or 
breakwater. 

5.  The  Spring  Tides  are  the  highest,  especially  those  which 
happen  36  hours  after  the  New  or  Full  Moon. 

6.  The   Neap  Tides   are  the  lowest,  especially  those  which 
happen  36  hours  after  the  Moon  is  at  one  of  its  quarters,  or  in 
quadrature,  to  speak  scientifically. 

7.  The  interval  of  time  between  noon  and  the  time  of  high 
water  at  any  particular  place  is  the  same  on  the  days  both  of 
New  and  Full  Moon.     The  precise  moment  of  high-water  at 
any  place  when  the  Moon  is  New  or  Full  is  called  by  French 
writers  IJetablissement  du  port,  and  that  expression  has  now 
been  brought  into  use  in  English  as  the  "  Establishment  of  the 
Port,"  an  awkward  phrase  which  in  itself  conveys  no  meaning 
till  explained. 

The  fact  that  an  interval  of  time  elapses  at  any  given  place 
between  the  meridian  passage  of  the  Moon  and  the  time  of 
high-water  is  due  to  another  fact,  namely,  that  the  waters  of  the 
oceari  are  retarded  by  friction  whilst  they  are  in  motion  over 
the  solid  surface  of  the  Earth  ;  and  so  it  comes  about  that  both 
the  lunar  and  the  solar  tidal  waves  are  not  found  immediately 
under  their  respective  luminaries,  but  follow  them  at  a  certain 
distance.  Moreover,  the  tidal  wave  is  affected  in  another  way 
by  the  action  of  both  these  luminaires,  and  at  certain  periods 


46  THE    TIDES. 

of  the  lunar  month  the  progress  is  either  accelerated  or 
retarded.  During  the  First  and  Third  Quarters  the  solar  tide  is 
W.  of  the  lunar  one  ;  and  consequently  the  actual  high-water 
due  to  the  combination  of  the  two  waves  will  be  to  the  W.  of 
the  place  at  which  it  would  have  been  if  the  Moon  were  acting- 
alone  ;  accordingly  the  time  of  high-water  will  be  accelerated. 
On  the  other  hand,  in  the  Second  and  Fourth  Quarters  the  Sun 
produces  a  retardation  in  the  time  of  high-water.  These  effects 
are  called  the  "  priming  "  and  "  lagging ;'  of  the  tides,  and  the 
effect  is  to  derange  the  average  retardation,  which  from  a  mean 
value  of  48  minutes  may  be  augmented  to  60  minutes  or 
be  reduced  to  36  minutes.  It  follows  from  this  that  a  sea- 
bather  who  is  watching  for  a  chance  of  getting  sand  and  not 
stones  for  his  foothold,  and  on  a  certain  day  does  just  escape 
the  stones,  will  not  of  necessity  on  the  next  day  find  himself 
exactly  in  the  same  pleasant  position  at  a  moment  which  is 
exactly  48  minutes  different  from  the  time  shown  by  his  watch 
on  the  previous  day. 

The  highest  Spring  Tides  occur  when  the  Moon  passes  the 
meridian  of  the  place  of  observation  about  i|  hours  after 
the  Sun,  for  then  the  maximum  effects  of  the  two  luminaries 
coincide. 

The  height  of  the  tides  is  affected  by  another  consideration — 
the  positions  of  the  Moon  and  the  Sun  with  respect  to  the 
Equator ;  the  nearer  these  two  bodies  are  to  the  Equator  the 
greater  the  height  of  the  tide.  Twice  a  year,  at  what  we  call 
the  Equinoxes — that  is  to  say,  about  March  21  and  September  22, 
speaking  roughly — the  Sun  is  actually  in  the  Equator.  If  at 
these  dates  the  Moon  should  be  in  or  near  the  Equator  the 
tides  will  be  the  highest  possible.  Such  tides  are  spoken  of 
as  the  Equinoctial  Spring  Tides.  On  the  other  hand  the 
smallest  tides  will  occur  at  about  the  Solstices  (June  21  and 
December  22)  if  the  Moon  attains  its  least  or  its  greatest 
meridian  height  at  the  same  time  as  the  Sun. 

Finally,  the  distances  of  the  Earth  from  the  Moon  and  the 


DETAILS   OF   THE   TIDES.  47 

Sun  also  affect  the  height  of  the  tides.  Other  things  being- 
equal,  the  height  of  a  tide  is  greater  or  less  according  as  the 
Moon  and  the  Sun  are  near  to  or  far  from  the  Earth. 
Accordingly  the  tides  at  or  near  December  22  are  higher 
than  those  at  or  near  June  21,  the  Earth  being  nearest  to  the 
Sun  (perigee  being  in  January)  and  farthest  from  the  Sun  in 
June  (apogee  being  in  July). 

Thus  far  in  our  consideration  of  the  tidal  wave  we  have 
been  keeping  up  the  fiction,  already  referred  to,  of  the  Earth 
being  a  ball  of  solid  matter  with  a  smooth  surface  and  covered 
all  over  with  a  layer  of  water  of  even  depth  everywhere.  It 
needs  not  to  be  pointed  out  that  this  is  pure  fiction,  some 
parts  of  the  Earth  being  land  and  other  parts  being  water,  the 
two  being  distributed  most  irregularly,  and  the  bottom  of  the 
Ocean  everywhere  being  of  varying  depth,  just  as  the  elevation 
of  the  land  is  everywhere  of  varying  height. 

These  facts  have  a  most  distracting  influence  on  the  times 
and  circumstances  of  the  movements  of  the  Earth's  water  ; 
and  though  the  rotation  of  the  Earth  on  its  axis  and  the 
movements  of  the  Moon  and  of  the  Sun  all  co-operate  in 
imparting  a  motion  of  translation,  so  to  speak,  to  the  Oceans 
of  water  which  exist  on  the  Earth,  local  circumstances  entirely 
destroy  the  theoretical  conditions.  In  other  words,  the  actual 
phenomena  of  the  tides  are  exceedingly  complicated,  and 
incapable  of  being  defined  by  cast-iron  rules  because  of  the 
irregular  outline  of  the  land,  the  uneven  surface  of  the  bed 
of  the  ocean,  and  the  action  of  winds  and  of  currents  of  air 
and  currents  of  water,  and  so  on. 

The  effect  of  all  these  disturbing  influences  cannot  be  better 
brought  home  to  the  mind  than  by  a  consideration  of  the 
following  details.  If  the  surface  of  the  Earth  were  entirely 
covered  by  the  hypothetical  layer  of  water  mentioned  on  a 
previous  page,  the  height  of  a  tide  raised  by  the  Sun's  attrac- 
tion would  be  i  ft.  ii  in.,  and  of  a  lunar  tide  4ft.,  but  the 
difference  in  the  level  of  the  waters  in  the  ocean  due  to  the 


48  THE    TIDES. 

disturbing  causes  just  spoken  of  <are,  in  the  vast  number  of 
cases,  entirely  different,  and  in  excess  of  these  figures.  In 
deep  estuaries  or  creeks  ending  in  narrow  channels,  which 
gradually  converge  inwards  as  a  common  wine-funnel  does, 
the  range  is  very  much  greater  than  along  an  open  shore. 
For  instance,  in  the  Bristol  Channel,  off  Chepstow,  the  range 
of  rise  and  fall  is  as  much  as  38  ft.,  and  in  some  similar 
situations  in  foreign  countries  the  range  is  even  greater. 

I  once  had  an  opportunity  of  standing  on  the  shore  of  the 
Bristol  Channel  on  the  Gloucester  side  of  Chepstow,  and  the 
rapidity  with  which  landmarks  such  as  piles  and  rocks,  near 
and  around  which  I  had  walked  a  few  minutes  previously,  were 
submerged,  and  deeply  submerged,  was  very  striking  to  me, 
whose  experience  of  the  rise  and  fall  of  the  tides  was  limited 
to  open  shores  on  the  South  and  East  of  England. 

Along  open  shores  the  rise  and  fall,  measured  in  feet,  are 
comparatively  limited,  especially  where  promontories  or  head- 
lands jut  out  into  the  sea.  Thus,  at  the  Needles  in  the  Isle  of 
Wight,  the  range  is  only  9  ft.,  whilst  at  Weymouth  it  is  even 
less,  being  only  7  ft.  On  flat  shores  which  bound  large  open 
expanses  of  water  such  as  the  Atlantic  and  Pacific  Oceans,  and 
confined  seas  like  the  Mediterranean,  the  elevation  of  the 
tidal  wave  is  to  be  measured  rather  by  inches  than  by  feet. 
Thus  at  Toulon  it  is  I  ft.  ;  at  St.  Helena  3  ft. 

The  barometric  pressure  of  the  atmosphere  is  also  a  factor 
to  be  taken  into  account  in  considering  the  probable  range  of 
the  tide  at  a  given  place  and  at  a  given  time.  When  the 
barometer  is  low  an  unusually  high  tide  may  be  expected,  and 
vice  versd  ;  and  it  has  been  estimated  that  a  depression  of 
i  in.  in  the  column  of  mercury  in  the  barometer  has  at  the 
London  Docks  the  effect  of  raising  the  level  of  the  tidal  water 
by  the  amount  of  7  in.,  which  at  Liverpool  would,  be  10  in. 
Thus  it  would  come  about  that,  supposing  an  unusual  high 
tide  in  the  Thames  (as  has  happened)  brought  the  water  up 
to  the  level  of  the  masonry  of  the  Thames  Embankment,  a 


ABNORMAL    TIDES.  49 

sudden  fall  of  the  barometer  might  unexpectedly  bring  the 
water  over  on  to  the  highway,  though  no  such  risk  had  been 
previously  contemplated.  The  influence  of  the  wind  also 
cannot  be  left  out  of  account,  for  it  is  often  very  potential 
either  in  aggravating  the  destructive,  effects  of  a  very  high  tide 
or  of  checking  them. 

It  is  in  the  Pacific  Ocean  and  among  the  South  Sea  Islands 
that  the  most  extraordinary  anomalies  in  connection  with  the 
tides  are  to  be  observed.  Many  travellers  and  navigators  who 
have  performed  voyages  in  those  parts  of  the  world  have 
recorded  their  strange  experiences.  I  have  come  across  many 
such  records,  and  transcribe  the  following  as  the  most  recent 
which  I  have  seen  : — 

"  This  is,  so  far  as  I  know,  the  only  part  of  the  world  [Tahiti] 
where  the  tide  is  high  but  once  a  day,  and  regularly  at  the 
same  hour — between  i  and  2  o'clock  in  the  afternoon.  The 
rise  and  fall  does  not  exceed  i  ft.  There  must,  I  suppose,  be 
a  corresponding  movement  of  the  sea  after  midnight.  It  may 
be  so  slight  that  the  regular  evening  breeze  retards  and 
renders  it  imperceptible.  I  have  often  questioned  nautical 
men  on  the  subject,  but  I  have  not  been  able  to  elicit  any 
satisfactory  explanations  :  nor  do  Nautical  Almanacs,  nor  the 
sailing  instructions  issued  by  the  Hydrographic  Department,  do 
more  than  chronicle  the  extraordinary  fact." l 

The  following  description  of  the  course  of  the  general  tidal 
wave  of  the  Earth  is  so  clear  and  concise  that  it  can  neither 
be  improved  upon  nor  be  abridged.  I  therefore  quote  it  in 
full  :.- 

"  The  Antarctic  is  the  cradle  of  tides.  It  is  here  that  the  Sun 
and  Moon  have  presided  over  their  birth,  and  it  is  here,  also, 
that  they  are,  so  to  speak,  to  attend  on  the  guidance  of  their 
own  congenital  tendencies.  The  luminaries  continue  to  travel 
round  the  Earth  (apparently)  from  east  to  west.  The  tides 
no  longer  follow  them.  The  Atlantic,  for  example,  opens  to 

1  E.  REEVES,  Broivn  Men  and  Women ;  or,  the  South  Sea  Islands,  p.  381, 
London,  1898. 


5O  THE   TIDES. 

them  a  long,  deep  canal,  running  from  north  to  south,  and, 
after  the  great  tidal  elevation  has  entered  the  mouth  of  this 
Atlantic  canal  it  moves  continually  northward  ;  for  the  second 
12  hours  of  its  life  it  travels  north  from  the  Cape  of  Good 
Hope  and  Cape  Horn,  and  at  the  end  of  the  first  24  hours  of 
its  existence  has  brought  high-water  to  Cape  Blanco  on  the 
west  of  Africa  and  Newfoundland  on  the  American  continent. 
Turning  now  round  to  the  eastward,  and  at  right  angles  to 
its  original  direction,  this  great  tidal  wave  brings  high-water, 
during  the  morning  of  the  second  day,  to  the  western  coasts  of 
Ireland  and  England.  Passing  round  the  northern  cape  of 
Scotland,  it  reaches  Aberdeen  at  noon,  bringing  high-water 
also  to  the  opposite  coasts  of  Norway  and  Denmark.  It  has 
now  been  travelling  precisely  in  the  opposite  direction  to  that 
of  its  genesis,  and  in  the  opposite  direction,  also,  to  the  relative 
motion  of  the  Sun  and  Moon.  But  its  erratic  course  is  not  yet 
complete.  It  is  now  travelling  from  the  northern  mouth  of 
the  German  Ocean  southwards.  At  midnight  of  the  second  day 
it  is  at  the  mouth  of  the  Thames,  and  wafts  the  merchandise 
of  the  world  to  the  quays  of  the  port  of  London.  In  the  course 
of  this  rapid  journey  the  reader  will  have  noticed  how  the  lines 
[on  the  map]  in  some  parts  are  crowded  together  closely  on 
each  other,  while  in  others  they  are  wide  asunder.  This 
indicates  that  the  tide-wave  is  travelling  with  varying  velocity. 
Across  the  Southern  Ocean  it  seems  to  travel  nearly  1000  miles 
an  hour,  and  through  the  Atlantic  scarcely  less  ;  but  near  some 
of  the  shores,  as  on  the  coast  of  India,  as  on  the  east  of  Cape 
Horn,  as  round  the  shores  of  Great  Britain,  it  travels  very 
slowly ;  so  that  it  takes  more  time  to  go  from  Aberdeen  to 
London  than  over  the  arc  of  120°  which  reaches  from  60"  of 
southern  latitude  to  60°  north  of  the  Equator.  These  differ- 
ences have  still  to  be  accounted  for;  and  the  high  velocities 
are  invariably  found  to  exist  where  the  water  is  deep,  while 
the  low  velocities  occur  in  shallow  water.  We  must  therefore 
look  to  the  conformation  of  the  shores  and  bottom  of  the  sea 
as  an  important  element  in  the  phenomena  of  the  tides."  l 

Theoretically,  if  the   whole   Earth  were   uniformly  covered 
with  water,  the  average  velocity  of  the  tidal  wave  round  the 

1  JOHNSON,  Physical  Atlas. 


TIDES    ON    THE    ENGLISH    COAST.  51 

Earth  would  be  rather  more  than  1000  miles  per  hour,  and 
the  writer  of  the  foregoing  extract  seems  to  think  that  this 
velocity  is  nearly  reached  in  the  Southern  Ocean,  where  there 
exists  a  vast  stretch  of  water  not  broken  in  upon  by  any 
important  masses  of  land. 

Though  1  have  mentioned  the  islands  of  the  Pacific  as 
localities  where  special  anomalies  exist  in  connection  with  the 
tides,  it  must  not  be  forgotten  that  much  nearer  home,  to  wit 
on  the  coasts  of  Hampshire  and  the  Isle  of  Wight  and  some 
other  localities,  some  strange  departures  from  the  normal  con- 
dition of  things  tidal  are  often  exhibited.  In  the  case  of  Hamp- 
shire, owing  to  the  fact  that  the  tides  in  the  Solent  and  at 
Spithead  do  not  run  easterly  on  the  flood  and  westerly  on 
the  ebb,  as  is  the  case  in  the  open  Channel,  but  run  from — 

Half-flood  to  half-ebb—easterly, 
Half-ebb  to  half-flood—westerly— 

— Southampton  and  places  up  Southampton  Water  have  four 
tides  in  the  24  hours  instead  of  two,  so  that,  after  flowing  to 
half-flood,  and  filling  up  with  the  west-travelling  tide,  when  the 
tide  changes  outside  Calshot  Castle,  there  is  a  slack  and  a 
partial  ebb,  until  the  eastern  tide  brings  enough  water  to  push 
the  flood  home  to  its  full.  Likewise  on  the  ebb,  when  the  tide 
changes,  there  is  a  slack  and  slight  flow,  until  the  suction  of 
the  west-going  tide  draws  the  water  away  down  Channel.1 

The  situation  of  the  Isle  of  Wight  as  an  island  opposite  an 
estuary  may,  no  doubt,  be  taken  to  suggest  that  similar  tidal 
vagaries  exist  elsewhere  in  the  world. 

As  regards  anomalies  elsewhere  in  the  British  Isles,  it  is 
stated  by  a  Scotch  writer  who  studied  very  closely  the  geo- 
graphical circumstances  of  the  West  of  Scotland  that  in  the 
strait  between  the  island  of  Isla  and  the  islets  of  Chenzie  and 

1  I  owe  the  foregoing  account  of  the  tides  in  the  Solent  to  Mr.  C.  G.  Brodie, 
F.R.A.S.,  an  experienced  yachtsman,  and  I  have  never  seen  this  information 
in  print. 


52  THE    TIDES. 

Oersa  the  time  occupied  by  the  ebb-tide  out  of  the  theoretical 
12  hours  is  lof  hours,  whilst  the  flood-tide  occupies  only  i| 
hours. 

The  last  matter  to  be  mentioned  in  connection  with  the  tides 
is  the  striking  and  remarkable  phenomenon  which,  bearing 
various  local  names,  is  commonly  called  in  English  a  "  Bore." 
It  is  to  be  seen  only  at  the  mouths  of  rivers  which  contract  at 
a  sharp  angle  from  a  wide  estuary  to  a  narrow  channel,  and 
happens  only  when  a  spring-tide  of  unusual  height  rushes 
up  the  estuary  into  the  narrow  channel,  carrying  all  before 
it  with  a  great  roar. 

From  all  accounts  the  bore  on  the  river  Tsien-Tang-Kiang, 
in  China,  must  be  regarded  as  one  of  the  most  remarkable  in 
the  world  ;  and  there  is  the  further  fact  attaching  to  it,  that 
it  has  been  made  the  subject  of  a  very  full  and  complete 
scientific  investigation  by  a  thoroughly  competent  observer, 
Admiral  W.  U.  Moore,  whose  account  was  communicated  in 
1889  to  the  Institution  of  Civil  Engineers.  His  remarks  are 
so  usefully  comprehensive  that  a  summary  of  them  will  make 
my  account  of  bores  in  general  much  more  complete  than  it 
could  otherwise  have  been.  [Plate  XXXIII.] 

To  begin  with  the  name  "bore."  The  Admiral  ascribes 
it  to  an  Icelandic  word  meaning  "billow."  It  is  also  called  in 
England  the  "hygre,"  and  "eagre";  also  "egre."  The 
Admiral  derives  '"  eagre "  from  the  French  "  eau-guerre,"  or 
"  water-war,"  which  sounds  ingenious,  whether  authentic  or  not. 
In  France  it  is  known  as  the  "  mascaret,"  and  in  Brazil  as 
the  "  pororoca."  It  seems  to  occur  in  6  or  8  rivers  in  the 
British  Isles,  including  the  Severn,  the  Wye,  the  Trent,  and 
the  Solway  ;  in  two  or  three  French  rivers — namely,  the  Seine, 
the  Garonne,  and  the  Loire  ;  in  some  of  the  Indian  rivers, 
including  the  Ganges,  the  Brahmaputra  and  the  Indus  ;  in 
the  branches  which  compose  the  mouth  of  the  Amazon  in 
S.  America  ;  and  in  one  river  at  least  in  China.  It  is  rarely 
observed  except  at  a  spring-tide,  and  as  a  rule  shows  itself 


THE 


53 


on  the  days  of  Full  and  New  Moon,  appearing  with  the  first 
of  every  flood-tide  for  3  or  4  days  succeeding  those  phases  ; 
after  which  the  tide  comes  in  with  only  a  swift  rush  unaccom- 
panied by  noise  or  violent  commotion. 

The  3  following  conditions  appear  to  be  necessary  to  create 
a  bore  : — 

1 .  A  swiftly  flowing  river. 

2.  An   extensive  bar  of  sand,  dry  at  low-water,  except  in 
certain  narrow  channels  kept  open  by  the  outgoing  stream. 

3.  The  estuary  into  which  the  river  is  discharged  must  be 
funnel-shaped,  with  a  wide  mouth  which   is  open   to  receive 
the  tidal  wave  coming  in  from  the  Ocean. 

If  either  of  these  3  conditions  is  wanting  there  will  be  no 
bore.  For  example,  in  the  case  of  the  Thames,  the  third 
condition  exists,  but  the  first  and  second  are  wanting  ;  for  the 
Thames  is  not  a  swift  river,  and  has  no  bar,  dry  at  low-water. 
In  the  Severn  all  3  conditions  are  found,  and  accordingly 
there  is  a  bore  ;  not  a  very  large  one,  it  is  true,  but  still  the 
most  noteworthy  in  the  British  Isles. 

The  bore  of  the  Tsien-Tang-Kiang  has  all  3  conditions 
well  developed.  The  estuary  into  which  the  river  falls  has  a 
vast  area  of  sand  at  its  head,  and  is  favourably  situated  for 
the  reception  of  the  incoming  tidal  wave  from  the  Pacific. 
The  range  of  the  tide  immediately  outside  the  Hang-Chau 
Gulf  is  12  ft.,  but  as  the  wave  becomes  compressed  in  advancing 
towards  its  head  at  the  end  of  the  navigable  waters,  it  is  as 
much  as  25  ft.  at  ordinary  spring-tides,  and  34ft.  when  there 
is  the  favourable  combination  of  a  wind  blowing  on  shore,  and 
a  Moon  in  perigee  at  the  time  of  Full  or  New.  The  navigable 
breadth  of  the  estuary  at  its  head  (where  the  tidal  wave  rises 
to  its  greatest  height)  is  about  ith  or  -|th  of  what  it  is  at  the 
mouth  ;  and  if  there  were  no  river  discharging  into  the  bay 
the  range  would  probably  be  60  ft.  or  70  ft.,  as  in  the  Bay  of 
Fundy. 

The  speed  of  the  advancing  tidal  wave  was  measured  by  the 


54  THE   TIDES. 

officers  of  H.M.S.  Rambler,  and  found  to  be  14^  statute  miles 
an  hour.  The  breadth  of  the  bore  is  about  I  mile,  and  its 
front  presents  the  appearance  of  a  gleaming  white  cascade  of 
bubbling  foam,  8  ft.  to  12  ft.  in  height.  The  noise  is  not  the 
least  impressive  feature  of  this  phenomenon.  On  a  calm  still 
night  it  can  be  distinctly  heard  14  or  15  miles  off,  and  more 
than  an  hour  before  it  arrives.  The  noise  increases  very 
gradually  until  the  bore  comes  abreast  of  an  observer  on  the 
bank  of  the  river,  when  he  has  to  endure  a  roar  but  little 
inferior  to  that  of  the  Rapids  below  Niagara.1 

South  America  seems  to  offer  an  example  of  a  bore  of  a  very 
remarkable  character.  The  following  description  of  a  bore  on 
the  river  Amazon  penned  by  La  Condamine  a  great  many 
years  ago  is  a  fitting  pendant  to  Admiral  Moore's  account  of 
the  Tsien-Tang-Kiang  bore  : — 

"  During  three  days  before  the  New  and  Full  Moons,  the 
period  of  the  highest  tides,  the  sea,  instead  of  occupying  six 
hours  to  reach  its  flood,  swells  to  its  highest  limit  in  one  or 
two  minutes.  The  noise  of  this  terrible  flood  is  heard  five  or 
six  miles  off,  and  increases  as  it  approaches.  Presently  you 
see  a  liquid  promontory  12  or  15  feet  high,  followeid  by 
another,  and  another,  and  sometimes  by  a  fourth.  These 
watery  mountains  spread  across  the  whole  channel,  and  advance 
with  a  prodigious  rapidity,  rending  and  crushing  everything  in 
their  way.  Immense  trees  are  sometimes  uprooted  by  it, 
and  sometimes  whole  tracts  of  land  are  swept  away." 

1  Abridged  and  added  to  from  Admiral  Moore's  paper  in  the  Minutes  of 
Proceedings  of  the  Institution  of  Civil  Engineers,  Session  1889-90,  vol.  xcix. 
Part  I.  A  still  more  detailed  account  will  be  found  in  the  Journal  of  the  China 
Branch  of  the  Royal  Asiatic  Society,  vol.  xxiii.  1888.  See  also  Sir  G.  H. 
DARWIN'S  Treatise  on  Tides. 


CHAPTER   V. 
THE  PLANETS  GENERALLY. 

What  the  planets  are. — May  be  conveniently  divided  into  two  groups. — 
The  Inferior  Planets. — The  Superior  Planets. — The  Minor  Planets. 
— Certain  planets  have  satellites. — The  purpose  served  by  them. — 
Certain  planets  have  phases. — The  planets  in  Conjunction. — The 
planets  in  Opposition. — Transits  across  the  Sun. — Characteristics 
common  to  all  the  planets. — Statement  of  these  by  Hind. — Kepler's 
Three  Laws. — Sir  J.  HerscheVs  statement. — Conjunction  of  two 
planets. — Instances  of  this. — Various  discarded  planetary  systems. 
— Suggested  I ntr a- Mercurial  and  Trans- Neptunian  planets. 

ROUND  the  Sun,  as  a  centre,  there  circulate  a  considerable 
number  of  bodies  which  we  call  planets l :  these  are  now 
known  to  be,  indeed,  many  hundreds  in  number,  but  we  can 
count  on  our  fingers  those  which  alone  are  worthy  of 
general  attention.  Those  which  are  known  to  everybody  and 
which  have  been  recognised  as  planets  from  the  earliest  times 
are  still  fewer  in  number,  and  comprise  only  Mercury,  Venus, 
the  Earth,  Mars,  Jupiter,  and  Saturn.  For  the  purposes  of 
astronomy  the  Earth,  though  strictly  a  planet  in  the  proper 
sense  of  the  word,  may  be  left  out  of  consideration,  because 
we,  being  on  the  Earth,  cannot  approach  its  study  in  the  same 
way  in  which  we  deal  with  the  other  planets  just  named.  The 
study  of  the  Earth  concerns  the  sciences  of  geography  and 
geology  in  particular,  and,  except  for  the  purpose  of  noting  its 
place  in  the  solar  system,  because  it  is  one  of  the  cortege  of 

1  Greek,  TrAaKJjTijs,  a  wanderer, 
55 


56  THE    PLANETS    GENERALLY. 

planets  which  travel  round  the  Sun,  the  astronomer  has  not 
much  concern  with  it.  He  uses  it,  however,  for  the  arbitrary 
purpose  of  separating  the  planets  into  two  groups,  putting  into 
one  group  those  which  are  nearer  the  Sun  than  the  Earth  and 
into  the  second  group  all  the  other  planets  outside  the  orbit  of 
the  Earth. 

The  former  are  called  "  Inferior "  planets,  and,  so  far  as  we 
know,  are  only  two  in  number,  namely,  Mercury  and  Venus  : 
the  others  are  called  "  Superior  "  planets,  and  include  not  only 
the  other  three  named  above  (Mars,  Jupiter,  and  Saturn),  but 
two  other  large  planets  still  farther  off,  Uranus  and  Neptune, 
together  with  some  700  miscellaneous  planets  known  as  the 
"  Minor "  planets,  which  circulate  round  the  Sun  in  orbits 
lying  between  Mars  and  Jupiter. 

It  will  be  readily  understood,  from  what  has  just  been  said, 
that  the  designations  "Inferior"  and  "Superior"  are  not  a 
little  misleading,  because  both  the  Inferior  planets  are  very 
much  larger  than  nearly  all  the  Superior  ones,  reckoned  in 
respect  of  their  numbers. 

There  is  another  important  distinction  between  the  two 
classes  of  planets.  The  Inferior  ones  have  no  satellites,  whilst 
all  the  large  Superior  ones  are  provided  with  attendants^ 
which  are  called  satellites,  though  frequently  spoken  of  as 
"moons,"  because  serving  the  purposes  served  by  our  Moon. 
This  distinction,  as  regards  the  possession  or  non-possession 
of  satellites,  may  possibly  be  ascribed  to  design  on  the  part 
of  the  Creator.  Mercury  and  Venus,  being  so  comparatively 
near  to  the  Sun,  do  not  need  the  benefit  afforded  by  a  satellite 
in  the  way  of  supplementary  light.  The  Earth,  as  we  have 
seen,  is  so  favoured  by  having  a  companion  to  afford  additional 
light,  and  probably  it  may  be  said  with  truth  that,  as  all  the 
other  Superior  planets  have  satellites,  and,  with  the  exception 
of  Neptune,  satellites  greater  in  number  than  the  Earth  has, 
such  satellites  may  be  regarded  as  performing  the  special  office 
of  supplying  in  some  degree  to  their  primaries  light  by  way 


MOVEMENTS    OF    THE    PLANETS.  57 

of  compensation  for  the  limited  amount  of  Sunlight  which  they 
receive  because  of  their  vast  distance  from  the  Sun.  There 
is  another  important  distinction  between  the  Inferior  and 
Superior  planets.  The  former  are  subject  to  phases  which 
are  identical  in  character  with  the  phases  of  the  Moon — 
Crescents,  Quarters,  Full,  and  so  on  ;  whilst  the  Superior 
planets,  with  the  exception  of  Mars  and  Jupiter  (in  a  slight 
degree),  exhibit  no  appreciable  phases. 

The  phases  of  Mercury  and  Venus  involve  the  consequence 
that  they  pass  round  the  Sun,  sometimes  on  this  side  of  the 
Sun  looked  at  from  the  Earth,  and  sometimes  on  the  farther 
side  of  the  Sun.  When  passing  on  our  side,  then,  at  the 
moment  at  which  Earth,  planet,  and  Sun  are  exactly  in  the 
same  straight  line,  the  planet  is  said  to  be  in  "Conjunction" 
with  the  Sun.  When  on  the  opposite  side,  with  the  Earth,  Sun 
and  planet  in  the  same  straight  line,  the  planet  is  said  to  be  in 
"  Opposition."  A  moment's  thought  will  make  it  evident  that 
when  in  these  two  positions  (and  also,  unless  they  are  at  a 
certain  distance,  on  either  side)  the  planets  will  be  lost  in 
the  Sun's  rays,  and  will  therefore  be  invisible  to  us. 

There  is  one  exception  to  the  rule  of  these  planets  being 
invisible  when  in  Conjunction,  and  that  is  when  either  of  them 
is  in  a  straight  line,  so  disposed  that  the  planet  may  be  seen 
actually  on  and  passing  across  the  Sun's  disc.  This  pheno- 
menon, which  is  rare,  constitutes  what  is  called  a  "  transit "  of 
the  planet.  But  the  consideration  of  this  in  detail  belongs  to 
a  later  chapter. 

The  circumstances  of  the  Superior  Planets  are  altogether 
different.  They  never  can  be  in  Conjunction  with  the  Sun  in 
the  same  sense  that  the  Inferior  Planets  can  be,  because  they  are 
always  going  round  the  Sun  in  orbits  outside  that  of  the  Earth. 
The  epoch  of  Conjunction  with  them  puts  them  in  a  straight 
line  but  in  a  different  order,  namely,  in  the  order  of  Earth,  Sun, 
Planet.  When  this  happens  they  are  invisible  from  the  Earth 
because  lost  in  the  Sun's  rays  ;  and  that  state  of  things  subsists 


58  THE    PLANETS    GENERALLY, 

for  a  certain  length  of  time  before  and  after  Conjunction, 
dependent  on  the  brilliancy  of  the  particular  planet  and  our 
optical  means  to  view  it  when  immersed  to  some  degree  in 
the  Sun's  rays,  which  means  in  some  degree  of  twilight. 

The  Superior  Planets  are  also  on  occasions  in  Opposition, 
but  here  again  the  term  has  not  quite  the  same  meaning  as  it 
has  when  applied  to  an  Inferior  Planet.  An  Inferior  Planet  is, 
as  we  have  seen,  lost  in  the  Sun's  rays  ;  but  a  Superior  Planet 
is  at  its  very  best,  so  far  as  the  Sun  is  concerned,  when  in 
Opposition,  because  it  is  on  the  meridian  at  midnight  when  the 
Sun  is  on  the  meridian  at  midday,  the  order  of  position  being 
Sun,  Earth,  Planet. 

The  only  Superior  Planet  subject  to  a  clearly  evident  phase 
is  Mars,  which  in  two  positions  in  its  orbit  (Quadratures, 
E.  and  W.)  suffers  a  slight  encroachment  first  on  one  side 
and  then  on  the  other  side  of  its  disc.  Theoretically,  Jupiter 
should  exhibit  a  slight  phase  under  analogous  conditions,  but 
it  is  not  very  easy  to  appreciate  it  ;  still,  it  must  be  deemed, 
when  at  its  quadratures,  to  be  slightly  gibbous  (as  the  term  is), 
but  much  less  so  than  Mars.  The  defalcation  of  the  light  is 
on  the  limb  of  the  planet  which  is  farthest  from  the  Sun. 

There  are  certain  characteristics  common  to  all  the  planets, 
which  have  been  stated  by  Hind  in  the  following  terms  : — 

i.  They  move  in  the  same  invariable  direction  round  the 
Sun,  their  course,  as  viewed  from  the  N.  side  of  the 
Ecliptic,  being  contrary  to  the  motion  of  the  hands  of  a 
watch. 

2.  They  describe  oval  or  elliptical  paths  round  the  Sun,  not, 
however,  differing  greatly  from  circles. 

3.  Their  orbits  are  more  or  less  inclined  to  the  Ecliptic,  and 
intersect  it  in  two  points,  which  are  the  "  Nodes,"  one  half  of 
the  orbit  lying  N.  and  the  other  half  S.  of  the  Earth's  path. 

4.  They  are   opaque  bodies,  like  the  Earth,  and   shine  by 
reflecting  the  light  which  they  receive  from  the  Sun. 

5.  They   revolve  upon   their  axes  in  the  same  way  as  the 


THE    ORBITS    OF    THE    PLANETS. 


59 


Earth.     This,  we  know  by  telescopic   observation,  to 

case    with    many    planets, 

and,  by  analogy,  the  rule 

may  be   extended   to    all. 

Hence  they  will  have  the 

alternation     of     day     and 

night,  like  the  inhabitants 

of    the   Earth  ;    but    their 

days  are  of  different  lengths 

to  our  own. 

6.  Agreeably  to  the 
principles  of  Gravitation, 
their  velocity  is  greatest  at 
those  parts  of  their  orbits 
which  lie  nearest  the  Sun, 
and  least  at  the  opposite 
parts  which  are  most 
distant  from  it  ;  in  other  | 
words,  they  move  quickest  > 
in  perihelion  and  slowest 
in  aphelion. 

Although    the  matter  is 
somewhat  technical',    I 
think   it   well    to    mention 
here,    in    order    to    make    I 
these   general    statements   | 
complete,    the   laws   regu-    w 
lating    the  movements    of  |» 
the     planets     which    * 
bear  the  name  of  Kepler.     1 
They    may   be    stated    as    s 
follows  : —  £ 

I.  The  planets  move  in  "g 
ellipses,  having  the  Sun  "* 
in  one  focus. 


be   the 


6o 


THE    PLANETS    GENERALLY. 


2.  The  radius-vector  of  each  planet  describes  equal  areas  in 
equal  times. 

3.  The   squares   of  the   periodic   times   of  the   planets   are 
proportional  to  the  cubes  of  their  mean  distances. 

These  laws  hold  good  for  all  the  planets,  and  also  for  all 
their  satellites  relatively  to  their  respective  primaries. 

A  few  words  may  be  added  to  make  these  laws  a  little  more 
clear  to  the  non-mathematical  reader.  Everybody  understands 

what  the  centre 
of  a  circle  is, 
and  that  from 
the  centre 
every  part  of 
the  circumfer- 
ence is  equi- 
distant; but,  in 
the  case  of  an 
ellipse,  there 
is  no  point 
inside  it  which 
is  equidistant 
from  the  cir- 
cumference ; 
and,  in  order 
to  draw  such  a 
figure,  one 

must  make  use  of  two  points  inside.     Each  of  these  points  is 
called   a  "focus." 

A  radius-vector  is  an  imaginary  line  drawn  from  the  Sun  to 
a  planet  at  the  circumference  of  the  ellipse  which  constitutes 
the  planet's  orbit.  The  statement  that  the  radius-vector  of 
each  planet  describes  equal  areas  in  equal  times  will  be  best 
grasped  by  an  inspection  of  Fig.  71,  where  the  shaded  portions 
represent  equal  areas,  whilst  the  distances  along  the  circum- 
ference, though  very  unequal  in  extent,  are  yet  traversed  by  the 


Fig.  71. — Diagram  illustrating  Kepler's 
Second  Law. 


KEPLER'S    LAWS. 


6t 


planet  in  equal  periods  of  time.  Such  is  the  case  because  every 
planet  moves  faster  when  nearest  the  Sun  than  it  does  when 
farthest  oft"  from  the  Sun. 

Kepler's  Third  Law  involves  a  curious  point  :  if  the  dis- 
tance of  the  Earth  from  the  Sun  be  taken  as  unity  (To),  and  its 
period  taken  in  days,  then  if  the  squares  of  the  periods  of  the 
planets  be  divided  by  the  cubes  of  their  mean  distances  from 
the  Sun,  the  result  in  quotients  will  be  the  same  substantially 
for  all  the  planets,  the  slight  discrepancies  in  the  quotients 
being  due  to  inexactness  in  the  observations  on  which  the 
calculations  are  based. 

This  law  applies  to  all  the  satellites,  so  that  an  identical 
quotient  will  be  obtained  for  each  group  of  satellites,  though, 
comparing  one  group  with  another,  the  quotients  will  vary 
inter  se. 

The  foregoing  statement,  calculated  for  the  planets,  is 
exhibited  in  the  following  table  : — 


Planet. 

Distance  from 
sun  :  a 

Period  in 
days  :  p 

P~ 

«a 

Mercury 

0-38710 

87-969 

»3342I 

Venus    .... 

072333 

224-701 

I334I3 

Earth     .... 

I  -OOOOO 

365  256 

133408 

Mars      .... 

1-52369 

686-979 

I334IO 

Ceres  (as  typical    Minor 

Planet)    . 

2*77692 

1679^55 

I322IO 

Jupiter  .... 

5-20277 

4332-5«5 

133294 

Saturn   .... 

9-5385* 

10759-220 

-33375 

Uranus  .... 

19-18239 

3068(3  821 

133422 

Neptune 

30-03627 

60126-722 

I334I3 

To  draw  an  ellipse,  the  following  points  must  be  borne  in 
mind,  The  eccentricity  of  an  ellipse  is  the  ratio  of  the 
distance  between  the  centre  and  either  focus  to  the  length  of 
the  semi-axis-major.  It  is  usually  given  as  a  decimal  fraction, 


62  THE    PLANETS    GENERALLY. 

the  semi-axis-major  being  taken  as  unity,  or  ro.  Thus,  an 
eccentricity  given  as  0-25  means  that  the  distance  between  the 
centre  and  either  focus  is  £th  of  the  semi-axis-major.  This  is 
sometimes  symbolised  by  the  Greek  letter  <£  and  with  an 
angular  measurement  named .  In  that  case  the  eccentricity  is 
obtainable  by  finding  from  the  tables  what  is  the  natural  sine 
of  the  angle  <£. 

In  order  to  draw  an  ellipse  of  a  prescribed  eccentricity  first  of 
all  draw  a  line  of  any  convenient  length  to  represent  the  axis- 
major  of  the  intended  ellipse  ;  bisect  it  and  mark  the  point  of 
bisection  ;  then  from  the  centre  set  off  in  each  direction  along 
the  line,  according  to  the  selected  scale,  distances  equal  to 
the  eccentricity ;  the  points  so  determined  will  be  foci  of  the 
required  ellipse.  Fix  pins  at  these  points  and  at  one  of  the 
extremities  of  the  axis,  and  then  proceed  as  follows.  Tie  a 
loop  of  cotton  or  silk  tightly  round  these  pins ;  remove 
the  pin  which  is  at  the  extremity  of  the  axis-minor ;  stretch 
the  thread  tightly  with  the  point  of  a  pencil  and  move  the 
pencil  round  under  the  guidance  of  the  thread  kept  tightly 
drawn. 

Perhaps  an  actual  example  in  figures  will  make  the  modus 
operandi  of  this  more  clear.  Say  you  want  to  draw  an  ellipse 
of  the  eccentricity  075.  Draw  a  line  10  inches  long  on  stiff 
white  paper  or  card-board  ;  bisect  it ;  set  off  on  each  side  of  the 
point  of  bisection  distances  of  3!  inches  (i.e.  7*5  half-inches) ; 
these  points  will  be  the  foci  of  the  required  ellipse.  Then 
proceed  with  the  aid  of  the  thread  as  above.  Of  course  any 
units  may  be  employed  in  devising  a  scale,  but  perhaps  inches, 
as  in  the  above  example,  will  generally  be  found  most  convenient 
when  it  is  desired  to  obtain  the  form  of  a  planetary  or  cometary 
orbit. 

Sir  John  Herschel  put  forth,  many  years  ago,  a  fancy  statement 
for  the  purpose  of  enabling  a  reader  to  obtain  a  rough  general 
idea  of  the  dimensions  of  the  solar  system  and  of  its  constituent 
planets.  The  statement  needs  some  revision  and  expansion, 


THE    DISTANCES    OF    THE    PLANETS. 


to  meet  present  circumstances—treatment  which  I  have  applied 
to  it  ;  and  I  now  present  it  in  the  following  form  : 

Imagine  a  large  open  common  ;  on  it  place  a  globe  2  feet  in 
diameter  by  way  of  representing  the  Sun  ;  Mercury  will  then 
be  represented  by  a  mustard-seed  at  a  distance  of  82  feet  ; 
Venus  by  a  pea  at  a  distance  of  142  feet ;  the  Earth  also  by  a 
pea  at  a  dis- 
tance of  215 
feet  ;  Mars 
by  a  small 
pepper -corn 
at  a  distance 
of  327  feet ; 
the  Minor 
Planets  by 
grains  of  sand 
at  distances 
varying  from 
500  to  600 
feet;  then  a 
moderate- 
sized  orange 
^th  of  a  mile 
distant  from 
the  central 
point  will 
represent 
Jupiter  ;  a 

small  orange  fths  of  a  mile,  Saturn  ;  a  full-sized  cherry  f ths  of 
a  mile,  Uranus  ;  and  lastly,  a  plum  i£  miles,  Neptune,  the  most 
distant  planet  yet  known,  though  astronomers  suspect  there 
exists  another  planet  still  farther  off  and  hope  one  day  to  find  it. 

Extending  this  scheme,  the  aphelion  distance  of  Encke's 
Comet  would  be  880  feet ;  the  aphelion  distance  of  Donati's 
Comet  6  miles,  and  the  nearest  fixed  star  7500  miles. 


Fig.  72.— Conjunction  of  Venus  and  Saturn, 
Dec.  19,  1845. 


64 


THE    PLANETS    GENERALLY. 


An  idea  of  the  absolute  movements  day  by  day  of  the  planets 
in  their  orbits  would  be  obtained  by  imagining  Mercury  to 
move  every  day  3  feet;  Venus  2  feet;  the  Earth  if  feet; 
Mars  i£  feet  ;  Jupiter  io£  inches  ;  Saturn  7^  inches  ;  Uranus 
5  inches ;  Neptune  4  inches.  These  figures  serve  also  to 
illustrate  the  fact  previously  mentioned  that  the  orbital  velocity 

of  a.  planet  de- 
creases as  its 
distance  from 
the  Sun  in- 
creases :  and 
by  a  vast 
stretch  of  the 
imagination  we 
might  suppose 
a  place  in  the 
Universe 
where  a  planet 
would  not 
move  round 
the  Sun  at  all  ; 
in  other  words, 
where  Gravita- 
tion would 
cease  so  far  as 
our  solar 
system  was 
concerned. 

A  matter   of 

some  interest,  as  a  spectacle,  is  the  occasional  conjunction  of 
two  or  three  planets  in  the  same  part  of  the  heavens.  It  is 
exceedingly  rare  to  get  more  than  two  planets  together  in  the 
same  field  of  a  telescope,  but  a  combination  of  two  only  is  not 
at  all  uncommon.  Besides  those  which  are  here  illustrated, 
some  more  recent  instances  may  be  mentioned. 


Fig.  73 — Conjunction  of  Mars  and  the  Moon, 
Sept.  28,  1909. 


CONJUNCTIONS    OF   THE    PLANETS.  65 

In  September  1878  Mercury  and  Venus  were  together  in 
the  same  field  of  the  telescope  for  some  hours.  According 
to  Nasmyth,  the  contrast  in  the  appearance  of  the  two  planets 
was  very  marked.  Venus  looked  like  clean  silver,  whilst  Mer- 
cury had  more  the  appearance,  of  lead  or  zinc.  This  last 
statement  is  rather  curious,  because  Mercury  is  generally 
credited  with  being  of  a  rosy  tinge. 

On  August  9,  1886,  Venus,  Saturn,  and  the  bright  star 
8  Geminorum  were  in  the  same  field. 

On  May  6  of  the  same  year  Venus  and  Mars  were  very 
close  to  one  another,  Venus  being  o°  5'  to  the  south. 

That  same  month  of  May  1906  yielded  two  other  con- 
junctions visible  in  telescopes  armed  with  low-power  eye- 
pieces having  large  fields. 

On  May  n  Venus  and  Jupiter  were  close  together,  Venus 
being  T  n'  to  the  N.  A  week  later,  on  May  18,  Mars  and 
Jupiter  were  closer  still  together,  Mars  being  i°  6'  N.  Such 
a  succession  of  planetary  conjunctions,  conspicuous  planets 
being  involved,  is  unique. 

On  August  17,  1911,  Mars  and  Saturn  were  within  21'  of 
each  other,  and  therefore  in  the  same  field.  McEwen,  at 
Glasgow,  remarked  that : — 

"  Saturn  presented  a  bright  chrome  colour  in  contrast  to  the 
bright  ochre  tint  of  Mars.  It  must,  however,  be  admitted  at 
a  first  glance  that  Mars  did  look  somewhat  insignificant  com- 
pared with  Saturn  with  its  rings,  although  to  the  naked  eye 
Mars  appeared  much  the  brighter  of  the  two  planets." 

An  observer  in  America,  Conroy,  at  Los  Angeles,  wrote 
much  to  the  same  effect  : — 

"  The  difference  in  the  colours  of  the  two  planets  was  not 
as  pronounced  as  I  had  supposed  it  would  be.  Mars  glowed 
with  his  usual  strong,  ruddy  hue.  To  the  naked  eye,  and 
still  more  in  a  field-glass,  Saturn  was  decidedly  yellow,  with 
a  greenish  tinge." 

5 


66  THE  PLANETS  GENERALLY. 

The  1 8th  century  produced  a  planetary  conjunction  which, 
if  correctly  recorded,  must  have  been  singularly  striking, 
for  it  is  said  that  Venus,  Jupiter,  Mars,  and  Mercury  were 
all  seen  together  in  the  same  field  of  the  telescope. 

Whilst  we  nowadays  clearly  understand  that  the  Sun  is  the 
centre  of  our  planetary  system,  yet  the  realisation  of  that  fact 
is  quite  a  thing  of  modern  times,  being  hardly  more  than  three 
centuries  old.  Our  system  has  been  called  the  Copernican 
System,  from  the  Polish  astronomer,  Copernicus,  who  gave  it 
shape,  though  not  quite  its  final  shape.  Up  to  his  time,  and 
indeed  for  a  century  or  more  later,  there  were  rival  systems 
in  the  field.  They  may  be  named  in  something  like  the  order 
of  date  as  the  Ptolemaic  System,  the  Egyptian  System,  and 
the  Tychonic  System.  But  it  seems  hardly  worth  while  to 
describe  these  in  detail. 

The  question  is  a  natural  one  :  Are  there  more  planets 
circulating  round  the  Sun  than  those  already  spoken  of?  It 
is  probably  true  to  say  that  there  are,  and  the  question  of  a  planet 
within  the  orbit  of  Mercury,  and  also  of  one  beyond  the  orbit 
of  Neptune,  are  matters  which  have  attracted  the  thoughts  of 
many  astronomers,  though  without  any  very  certain  results. 

The  romance  of  an  intra-Mercurial  planet  caused  great 
searchings  of  heart  50  odd  years  ago,  and  many  were  fas- 
cinated with  the  story  of  the  French  doctor,  Lescarbault.  The 
idea  of  a  Trans- Neptunian  planet  has  not  yet  reached  the  stage 
of  romance,  much  less  that  of  fascination. 


CHAPTER   VI. 

THE  MOST  INTERESTING  AND  FAMILIAR 
PLANETS. 

A  classification  of  the  planets. — Mercury. — Difficult  to  observe. — 
Spots. — Phases. — Schiaparelli's  observations. — A  xial  rotation. — 
Statistics. — How  to  find  Mercury  or  Venus. — Venus. — Movements 
resemble  those  of  Mercury. — Physical  Features. — Possible  moun- 
tains.— A  tmosphere. — A  lleged  satellite. — Phases. — Galileo's  ana- 
gram.— Statistics. — Mars. — The  Earth's  nearest  neighbour. — Cele- 
brated for  its  colour. — Subject  to  a  slight  phase. — This  planet  very 
accessible  for  observation. — Its  apparent  movements. — Physical 
appearance. — Much  controversy  as  to  this. — Polar  snows. — Spots. — 
Markings  very  permanent. — Its  colour. — Satellites. — Statistics. — 
Jupiter. — Easy  of  observation. — The  largest  planet. — Belts. — Spots. 
— Jovian  spots  and  Sun-spots. — Satellites. — Large  ones  easily  found 
and  followed. — Small  ones  very  difficult. — Phenomena. — Velocity 
of  light. — Statistics. — Saturn. — Its  rings. — General  description  of 
them. — How  designated. — Changes  in  the  appearance  of  the  rings 
from  time  to  time. — Some  details  respecting  them. — The  ball. — 
The  satellites  as  tests  for  telescopes. — Statistics. 

THE  classification  of  the  planets  in  a  previous  chapter  into 
<  Inferior'  and  'Superior,'  though  desirable  from  a  scien- 
tific point  of  view,  is  not  one  which  appeals  much  to  the 
popular  observer  of  astronomical  phenomena,  who  is  con- 
cerned more  particularly  with  what  he  is  able  to  see. 
Accordingly,  it  will  be  convenient  to  adopt  now  a  new  classi- 
fication, which  cuts  across  the  previous  one,  because  of  its 
being  framed  upon  quite  a  different  basis.  Whilst  one  group 
responds  readily  to  the  general  title  of  the  "  Interesting  and 
Familiar  Planets,"  it  would  be  somewhat  unphilosophical  to 

67 


68       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

gibbet  the  residue  as  the  "  Uninteresting  Planets,"  for  the 
statement  would  not  be  true  of  some  of  them,  and  I  can  only 
give  them  the  vague  title  of  "planets  which  do  not  attract 
the  notice  of  the  generality  of  readers." 

Under  the  title  of  "  Interesting  and  Familiar  Planets "  I 
shall  deal  with  Mercury,  Venus,  Mars,  Jupiter,  and  Saturn,  all 
of  them  shining,  as  a  rule,  with  a  sufficient  amount  of  general 
brightness  to  attract  the  notice  of  almost  everybody  from  time 
to  time ;  but  Venus,  Mars,  and  Jupiter,  under  all  circum- 
stances, do  so  most.  Mercury  and  Venus,  being  within  the 
orbit  of  the  Earth,  can  never  be  very  far  from  the  Sun.  Venus, 
however,  on  occasions,  shines  with  such  splendour  that  twi- 
light has  no  appreciable  effect  in  impairing  it.  Mercury, 
however,  being  so  much  nearer  the  Sun  than  Venus,  is  more 
difficult  to  find  and  follow,  because  it  is  never  out  of  bright 
twilight.  The  other  planets  belonging  to  this  chapter — Mars, 
Jupiter,  and  Saturn — are  all  intrinsically  bright,  especially  Mars, 
and,  as  they  wander  all  over  the  heavens,  one  or  other  of 
them  is  almost  always  in  view  at  some  hour  of  a  given  night. 
Inasmuch  as  all  these  five  planets  have  special  features  of 
their  own,  it  will  be  well  to  give  them  sections  of  this  chapter 
to  themselves. 

MERCURY. 

Mercury  does  not  receive  much  attention,  owing  to  the  diffi- 
culty of  seeing  it,  as  already  stated.  Its  greatest  possible 
elongation  or  distance  from  the  Sun  not  exceeding  27°  45' 
(and  it  being  in  general  much  less),  the  difficulty  is  obvious. 
The  greatest  possible  elongation  on  the  E.  side  happens  at 
the  end  of  March  or  beginning  of  April,  Mercury  being  an 
"evening  star";  whilst  the  greatest  possible  elongation  on 
the  W.  side  happens  in  September,  when  Mercury  is  a 
"  morning  star." 

The  chances  of  seeing  it  are  best  for  us  in  England  when 
an  elongation  coincides  with  a  northerly  position  of  the  planet 


MERCURY.  69 

in  declination,  even  though  the  elongation  is  less  than  it 
might  be  at  other  times.  It  may  often  be  seen  with  the  naked 
eye,  shining  with  pink  or  rosy  light.  It  was  so  seen  by  many 
observers  in  April  1905. 

The  observations  of  Schroter  at  Lilienthal,  and  of  Sir  VV. 
Herschel,  led  them  to  think  they  had  obtained  decisive 
evidence  of  high  mountains  on  the  planet's  surface,  and  that 
one  in  particular  in  its  southern  hemisphere  manifested  its 
presence  by  the 
planet's  southern 
horn  having  a 
truncated  (or 
blunted)  appearance 
near  Inferior  Con- 
junction, which 
might  be  due  to  a 
mountain  obstruct- 
ing the  light  of  the 
Sun  from  reaching 
as  far  as  the  point 
to  which  the  cusp 
theoretically  ex- 
tended. 

Denning,  in  1882, 
saw     some     dark 
irregular  spots  upon    Fig.  74.— Mercury,  Sept.  17,  1885.  (Gttiot.) 
the   planet ;    also   a 

brilliant  spot  and  a  large  white  area.  The  southern  horn 
was  also  much  blunted.  He  states  that  his  results  led  him 
to  infer  that  the  markings  upon  Mercury  are  far  more 
decided  and  more  easily  discernible  than  those  of  Venus, 
and  that  Mercury's  surface  resembles  in  physical  appearance 
that  of  Mars.  A  French  observer,  Guiot,  in  1885,  remarked 
on  September  17  that  both  the  horns  of  Mercury  (then  almost 
a  semicircle)  were  truncated  j  but  that  only  the  southerji  horn 


70       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

was  so  five  days   later.     He   mentions   no   signs   of  shading 
or  spots. 

I  have  already  stated  in  a  previous  chapter  that  Mercury  is 
subject  to  phases,  and  will  repeat  here  the  bare  fact  only  by 
way  of  reminder  ;  and  will  merely  add  that  it  has  sometimes 
been  found  that  the  illuminated  portion  is  less  than  it  should 
be,  according  to  calculation.  This  statement  rests  upon  the 
testimony  of  some  competent  observers,  and  remains  un- 
explained. Explanation  is  the  more  difficult  because  there  is 
no  sufficient  evidence  that  Mercury  possesses  an  atmosphere. 

There  is  some  ground  for  the  opinion  that  it  is  more  easy  to 
notice  the  appearance  of  this  planet's  surface  than  is  the  case 
with  Venus.  More  than  one  observer  besides  Denning,  quoted 
above,  has  gone  so  far  as  to  suggest  that,  if  viewed  under 
favourable  circumstances,  the  surface  presents  an  aspect  more 
nearly  resembling  that  of  Mars  than  any  other  planet. 

The  astronomer  who  in  recent  times  has  made  the  most 
systematic  study  of  Mercury  is  Schiaparelli,  some  of  whose 
conclusions  are  rather  startling.  First  of  all,  he  considered  his 
best  chances  of  studying  the  planet's  surface  to  be  when  the 
Sun  is  above  the  horizon,  and  that  the  resulting  inconvenience 
is  less  distracting  than  the  tremors  which  manifest  themselves 
when  the  planet  is  viewed  low  down  towards  the  horizon  when 
the  sun  is  absent.  He  thought,  indeed,  that  some  of  the  mark- 
ings which  he  noticed  were  permanent  ;  hence  the  supposed 
analogy  between  Mercury  and  Mars.  But  the  most  sen- 
sational of  Schiaparelli's  conclusions  is  that  Mercury's  axial 
rotation  takes  place,  not  in  the  24  hours,  or  thereabouts, 
generally  supposed,  but  in  88  days,  being  the  period  occupied 
by  the  planet  in  going  round  the  Sun. 

This  conclusion  is  mentioned  because  of  Schiaparelli's  ex- 
perience and  standing  as  an  observer,  but  it  is  impossible  to 
accept  it  in  the  present  state  of  our  knowledge,  though  some 
other  observers,  including  Lowell,  in  1896,  have  seemed  in- 
clined to  agree  with  Schiaparelli, 


MERCURY.  71 

By  means  of  a  dark  spot  seen  in  April  1904,  McHarg  fixed 
the  period  of  rotation  at  24  h.  8  m.,  which  accords  with  all 
previous  values  except  Schiaparelli's. 

Mercury  revolves  round  the  Sun  in  almost  exactly  88  days 
at  a  mean  distance  of  about  36,000,000  miles,  which  may 
vary  between  the  limits  of  43,347,000  miles  and  28,570,000 
miles.  These  great  extremes  in  the  distance  of  Mercury  from 
the  Sun  at  different  times  are  due  to  the  great  eccentricity  of 
the  planet's  orbit,  which  is  greater  than  that  of  any  of  the  older 
planets,  though  exceeded  by  many  of  the  Minor  Planets  dis- 
covered in  modern  times.  The  apparent  diameter  of  Mercury 
varies  between«4^"  in  Superior  Conjunction  and  13"  in  Inferior 
Conjunction.  The  real  diameter  may  be  taken  to  be  about 
3000  miles,  or  perhaps  a  little  less. 

It  may  be  useful  to  many  of  my  readers  to  suggest  to  them 
a  convenient  method  for  finding  either  Mercury  or  Venus  in 
daylight  by  means  of  a  telescope  unprovided  with  an  equatorial 
mounting  or  circles.  For  the  successful  use  of  the  method 
certain  favourable  but  simple  conditions  respecting  the 
telescope  and  the  planets  are  required.  The  telescope  must 
be  perfectly  steady  on  a  substantial  stand,  and  anchored  in 
some  way  so  that  it  will  not  move  after  having  been  once 
placed  in  a  definite  position,  to  be  presently  named  ;  and  it 
must  be  provided  with  an  eye-piece  of  low  power  having  the 
largest  possible  field.  The  planet  to  be  sought  must  have  a 
declination,  which  shall  not  differ  more  than  about  3°  or  so 
from  that  of  the  Sun,  and  the  planet's  right  ascension  must  be 
greater  than  that  of  the  Sun.  If  the  difference  of  declination 
much  exceeds  3°  the  chances  of  picking  up  the  planet  will  be 
much  diminished. 

The  above  conditions  being  fulfilled,  the  method  consists  in 
using  the  Sun  to  find  the  position  in  the  sky  which  corresponds 
with  the  planet's  declination  ;  and,  the  telescope  being  pointed 
to  what  is  believed  to  be  about  the  planet's  declination,  the 
Observer  h^s  only  to  wait  until,  by  the  rotation  of  the  Earth, 


72       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

the  planet  is  brought  into  the  field  of  the  telescope.  Two 
further  preliminaries  must  be  observed  :  the  telescope  must  be 
carefully  focussed  either  on  a  Sun-spot  or  by  means  of  the 
Sun's  limb.  A  dark  glass  must  be  used  in  doing  this,  and 
when  this  has  been  done  a  pale  neutral  glass  should  be  used 
whilst  the  planet  is  being  swept  for. 

Accurate  focussing  of  the  telescope  is  very  important  ;  other- 
wise the  planet  may  escape  the  eye  which  is  looking  for  it, 
because  a  diffused  unage  is  easily  overlooked.  The  focussing 
having  been  assured,  the  Sun  must  be  carefully  brought  into 
the  centre  of  the  field,  and  the  line  along  which  it  travels 
into  and  out  of  the  field  must  be  carefully  noted.  This  is 
done  most  easily  if  the  eye-piece  of  the  telescope  is  provided 
with  two  wires  crossing  each  other. 

The  Sun  having  been  brought  to  the  centre  of  the  field,  the 
telescope  must  be  moved  upwards  (or  downwards)  at  right 
angles  to  the  apparent  line  of  the  Sun's  movement  by  the 
amount  of  the  difference  (estimated  from  the  centre  of  the  Sun) 
between  the  Sun's  right  ascension  and  the  planet's  right 
ascension,  the  centre  of  the  field  being  taken  in  both  cases  as 
the  point  aimed  at. 

No  circles  being  available,  the  observer  should  remember 
that,  the  diameter  of  the  Sun's  disc  being  approximately  £°, 
the  telescope  must  be  moved  vertically  by  as  many  half- 
degrees  as  equal  the  difference  between  the  declinations 
of  the  Sun  and  the  planet  respectively.  For  instance,  if 
the  difference  is  2^°,  the  telescope  must  be  moved  by  the 
amount  of  5  diameters  of  the  Sun.  The  observer  has  now 
nothing  more  to  do  but  to  wait  with  his  eye  at  the  telescope 
until  there  has  elapsed  the  time  in  minutes  which  is  the 
amount  of  difference  between  the  R.A.  of  the  Sun  and  that  of 
the  planet.1 

1  For  further  details  and  examples  of  this  method,  which  was  put  forward 
by  Dr.  R.  J.  Ryle,  see  The  Journal  of  the  British  Astronomical  Association, 
vol.  xv.  p.  TOO,  December  1904. 


FIGS.  75-77 


PLATE    XXIV. 


72] 


FIG.  78 


PLATE    XXV. 


The  Various  Phases  of  Venus. 


[73 


VENUS. 


73 


VENUS. 

What  has  been 
said  already  with 
respect  to  Mercury 
will  have  paved  the 
way  for  some  of  the 
things  which  will  now 
have  to  be  said 
respecting  Venus  ; 
but,  as  regards  one 
matter — its  brilliancy 
on  occasions — Venus 
stands  out  in  advance 
of  all  the  planets. 
Such  is  the  case 
especially  whenever 
we  look  at  it  in  the 
evening  or  the 
morning,  fulfilling 
the  functions,  in 
popular  parlance,  of 
the  "  evening  star " 
or  the  "  morning 
star."  But  on  certain 
occasions,  at  rare 
intervals,  when  the 
planet  is  at  or  near 
its  greatest  N.  Lati- 
tude and  about  5 
weeks  from  Inferior 
Conjunction,  it  shines 
with  surpassing 
splendour,  equal  to, 
or  even  greater  than, 


Fig.  79. — Venus  near  its|inferior 
conjunction.  (Schroter.) 


Fig.  80.— Venus,  Dec.  23,  1885. 

(Lihou.) 


74      THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

that  of  Sirius  (a  Canis  Majoris).  This  only  happens  about 
once  in  £  years,  and  occurred  last  in  1910,  and  will  recur 
in  1918.  The  brightness  is  sometimes  such  that  the  planet 
casts  a  shadow.  Such  was  the  case  on  January  12,  1902,  as 
recorded  by  Giacobini  at  Nice. 

The  further  fact  will  therefore  seem  to  follow  quite  naturally 
that  the  planet  is  often  readily  visible  in  the  daytime,  especially 
if,  by  means  of  graduated  circles,  the  seeker  knows  exactly 
where  to  look  for  it.1  ,  It  is  the  opinion  of  those  who  have  made 
a  special  study  of  Venus  that,  on  account  of  its  brilliancy,  it  is 
easier  to  detect  its  physical  features  by  daylight,  or  in  quite 
early  twilight,  rather  than  when  it  has  a  dark  sky  behind  it. 
These  features  include  shadings  or  patches  of  shade,  and  the 
truncature  of  one  or  both  horns  when  the  planet  shows  as  a 
crescent ;  and  these  facts  indicate  beyond  doubt  not  only.that 
the  visible  surface  is  not  even,  but  that  mountains  exist  on  it. 
It  is  not,  however,  usual  to  speak  definitely  of  the  existence  of 
mountains,  less  precise  words,  such  as  markings,  or  shadings, 
or  spots  being  used. 

A  Portuguese  observer,  M.  Lacerda,  has  stated  that  the 
southern  horn  is  always  longer  than  the  northern  one  ;  that 
is  to  say,  that  the  northern  one  is  often  more  blunt  than  the 
southern  one.  The  same  observer  remarked  that  the  most 
favourable  times  for  viewing  the  planet  were  always  between 
half  an  hour  before  and  one  hour  after  sunrise  ;  and  that  the 
corresponding  times  at  sunset,  when  the  planet  was  in  the  W., 
never  afforded  him  such  good  results. 

As  regards  the  physical  appearance  of  the  surface  of  Venus 
the  difficulties  are  very  much  the  same  as  those  which  are 
encountered  in  viewing  Mercury,  and  the  visual  results  are  not 
very  different ;  that  is  to  say,  in  addition  to  the  blunted  horns 
already  mentioned,  spots  are  visible  from  time  to  time. 

It  is  from  these  facts  that  the  conclusion  has  been  drawn 
that,  as  in  the  case  of  Mercury,  mountains  probably  exist ;  but 

1  S$e  p.  71,  ante. 


VENUS.   '-  75 

there  is  a  conflict  of  opinion  as  to  whether  these  mountains 
have  an  objective  existence  on  the  body  of  the  planet,  or 
whether  the  shadings,  which  have  been  assumed  to  be  moun- 
tains, are  merely  shadings  in  an  atmosphere  which  simulate 
mountains. 

The  fact  that  Venus  has  an  atmosphere  of  considerable 
density  seems  well  established,  especially  by  the  appearance 
presented  by  the  planet  when  under  observation  during  transit 
across  the  Sun.  A  further  proof  of  the  existence  of  an  atmo- 
sphere was  furnished  on  July  26,  1910,  on  the  occasion  of  an 
occultation  of  the  star  rj  Geminorum  by  the  planet.  The  star's 
brightness  diminished  rapidly  during  2  or  3  seconds  before 
immersion,  and  increased  rapidly  during  i£  or  2  seconds  after 
emersion.  It  was  thought  by  the  French  observers  who  noted 
these  results  that  a  variation  of  light  during  2  seconds  would 
be  explained  by  the  existence  of  an  atmosphere  about  68  mik  s 
in  height.  There  is  such  a  considerable  coincidence  in  the 
various  figures  arrived  at  as  regards  Venus's  atmosphere  that 
its  reality  and  considerable  extent  are  open  to  no  doubt.  Per- 
haps even  it  is  more  dense  than  that  of  the  Earth. 

When  Venus  is  near  its  Inferior  Conjunction  there  may 
sometimes  be  noticed  an  appearance  not  unlike  the  Lumiere 
cendree,  or  "ashy  light,"  frequently  visible  when  the  Moon 
exhibits  a  narrow  crescent,  as  mentioned  in  the  previous 
chapter.  (Ante,  p.  36.) 

Though  this  phenomenon  has  been  seen  and  recorded  by 
many  observers  during  a  long  period  of  time,  the  most  careful 
and  complete  observations  are  those  which  were  made  by 
Zenger  at  Prague  in  1883.  Without  quoting  the  details  gener- 
ally which  he  noted,  it  may  suffice  to  state  that  he  considered 
all  the  phenomena  which  are  presented  by  Venus  when  its  disc 
is  partly  illuminated  and  partly  unilluminated  find  a  complete 
counterpart  in  what  we  see  when  scrutinising  the  Moon  ;  and 
that  the  varying  tinges,  sometimes  simply  dark,  are  analogous 
tp  what  we  often  see  in  looking  at  a  "young"  Moon,  or  the 


j6       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

Moon  eclipsed.  In  other  words,  that,  as  we  know  the  variations 
in  the  Moon's  appearance  which  we  see  from  time  to  time 
under  such  circumstances  depend  on  the  varying  conditions  of 
the  Earth's  atmosphere,  so  the  different  appearances  presented 
by  Venus  depend  upon  the  varying  conditions  of  the  atmo- 
sphere of  Venus.  We  have  seen  that,  in  the  case  of  Mercury, 
the  measured  breadth  of  its  phase,  when  half  illuminated,  does 
not  always  accord  with  the  theoretical  breadth  which  ought 
to  be  shown  at  that  particular  stage.  The  same  discrepancy 
occurs  in  the  case  of  Venus. 

There  once  raged  a  long  controversy,  spread  over  many 
years  during  the  i8th  century,  as  to  whether  Venus  had 
a  satellite.  The  testimony  to  that  effect  was  varied  and 
strenuous,  and  proceeded  from  many  observers  ;  but  there  is 
now  no  question  but  that  they  deceived  themselves,  and  in  their 
small  telescopes  mistook  stars  for  companions  to  the  planet,  for 
it  is  quite  certain  that  if  Venus  did  possess  a  satellite,  it  would 
have  been  recognised  long  ago  in  some  of  the  many  great 
telescopes  which  were  brought  into  use  in  the  second  half  of  the 
igth  century. 

The  planet  Venus  has  always  occupied  a  prominent  place  in 
the  literature  of  poets  and  historians  during  more  than  two 
thousand  years.  It  would  occupy  too  much  space  to  offer  any 
quotations,  but  there  is  one  literary  trick  (I  can  use  no  better 
word)  which  is  associated  with  the  planet  and  which  deserves 
mention,  especially  because,  as  we  go  along,  we  shall  find  that 
the  same  trick  confronts  us  in  the  case  of  another  planet.  In 
olden  times,  say  three  centuries  ago,  before  the  days  of  Copy- 
right and  Patent  Laws  and  "  Merchandise  Marks  Acts,"  when 
a  man  discovered  something  the  honour  of  which  he  desired  to 
attach  to  his  own  name,  he  announced  it  in  obscure  phrase- 
ology, which  secured  him  the  priority  of  credit  without  disclosing 
his  discovery  in  detail.  Thus  it  was  that  Galileo,  who  dis- 
covered the  phases  of  Venus,  is  said  to"  have  announced  his 
discovery  in  the  following  Latin  logogriphe,  or  anagram  ; 


FIGS.  81-86 


PLATE    XXVI. 


March   22,  6  h. 


March   26,   7  h. 


March   28, 


March  30,  6f  h. 


March  31,  6^  h. 


76] 


Venus,  1881  (W.   F.  Denning). 


April  5,  6J  h. 


FIGS.  87-92 


PLATE    XXVII. 


May  14,  8J-  in  spec.  (W.  F.  Gale).     April  14,  i2|  in  spec.  (P.  B.  Molesivorth). 


April  19,  g\  in  spec.  (T.  E.  R.  Phillips).     April  21,  2\  in  spec.  (P.  B.  Molesworth). 


May  21,  5  in  O.G.  (tf.  /ft/M/*).          April  8,  6J  in  spec.  (//.  Carder). 

Mars,  1903.  [77 


VENUS.  77 

"  Haec  immatura  a  me,  jam  frustra,  leguntur — oy "  ("These 
things  not  ripe  ;  at  present  [read]  in  vain  [by  others]  are  read 
by  me  "  ),  the  "  me  "  being  Galileo. 

This  Latin  sentence,  when  transposed,  becomes  :  "  Cynthia 
figuras  aemulatur  Mater  Amorum  "  ("  The  Mother  of  the  Loves 
[Venus]  imitates  the  phases  of  Cynthia  [the  Moon]  "). 

The  letters  "  oy  "  are,  it  will  be  observed,  redundant,  so  far 
that  they  cannot  be  made  use  of  in  the  transposition. 

There  seems  reason  to  believe  that  the  special  brightness  of 
Venus  at  its  best  is  due  to  some  exceptional  condition  of  things 
which  enables  it  to  reflect  a  larger  proportion  of  the  Sun's  rays 
falling  upon  it  than  is  the  case  with  Mercury. 

It  is  good  practice  for  an  amateur  to  try  and  ascertain  up  till 
how  long  before^  and  how  soon  after,  Inferior  Conjunction  he 
can  see  Venus  in  a  telescope.  The  interval  ought  only  to  be 
one  of  hours,  and  not  many  of  them. 

Venus  travels  round  the  Sun  in  224  days  at  a  mean  distance 
of  67,020,000  miles.  The  orbit  is  nearly  that  of  a  circle, 
its  eccentricity  being  the  smallest  of  all  the  orbits  of  the 
large  planets,  but  several  minor  planet  orbits  are  more  nearly 
circular.  The  apparent  diameter  of  Venus  varies  between  9" 
in  Superior  Conjunction  and  65"  in  Inferior  Conjunction.  At 
its  elongations  its  apparent  diameter  is  25".  The  real  diameter 
is  about  7500  miles  ;  that  is  to  say,  Venus  is  nearly,  but  not 
quite,  so  large  as  the  Earth.  The  period  of  its  axial  rotation 
is  disputed,  but  it  probably  amounts  to  about  23!  hours. 

MARS. 

We  will  now  proceed  to  the  important  planet,  Mars,  passing 
over  the  Earth  for  the  reasons  already  given  :  that,  though  the 
Earth  is  a  planet,  and  a  very  important  one  too,  we  cannot, 
because  we  are  on  it,  study  its  appearance  in  the  way  in  which, 
with  the  assistance  of  telescopes,  we  study  the  appearance  of 
other  planets. 


78       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

Mars  and  Jupiter,  which  will  occupy  our  attention  in  the  next 
section,  are  the  planets  which  most  often  attract  our  notice 
in  the  sky  by  night  because  one  or  other  of  them  is  almost 
always  visible  at  some  time  or  other  between  sunset  and 
sunrise.  Moreover,  Mars,  by  reason  of  its  normal  fiery  colour, 
can  never  be  mistaken,  or  at  any  rate  should  never  be  mis- 
taken, for  any  other  planet  or  for  any  star. 

Mars  exhibits,  on  occasions,  a  slight  phase,  but  it  is  not 
very  noticeable.  When  the  planet  is  in  Opposition — that  is  to 
say,  is  on  the  meridian  at  midnight— it  presents  a  perfectly 
circular  disc  ;  but  at  other  times  it  is  gibbous,  the  maximum 
defalcation  of  light  occurring  when  the  planet  is  in  Quadra- 
ture, or  6  hours  away  from  the  Sun,  either  E.  or  W.  At 
these  epochs  the  planet  resembles  the  Moon  3  days  on  either 
side  of  the  epoch  of  Full  Moon. 

By  reason  of  its  proximity  to  the  Earth,  it  comes  into 
Opposition  about  once  in  every  two  years,  or,  to  be  more 
exact,  every  780  days,  this  being  what  is  called  its  "synodic 
period."  When  in  perihelion  (that  is,  nearest  to  the  Sun) 
and  in  perigee  (that  is,  nearest  to  the  Earth)  at  the  same 
time,  which  coincidence  occurs  every  15  years,  Mars  rivals 
Jupiter  in  brilliancy.  This  happened  last  in  the  summer  of 
1909,  and  will  not  occur  again  until  1924.  But  the  fact  that 
we  get  a  good  view  of  Mars  at  the  short  interval  of  every  two 
years  gives  us  great  facilities  for  studying  it,  and  should  be 
an  encouragement  to  tracing  its  movements  in  the  heavens 
amongst  the  stars.  This  is  not  so  conveniently  done  in  the 
case  of  the  other  Superior  Planets  because  they  take  so  many 
more  years  in  making  their  circuits  round  the  Sun,  and  move 
so  much  slower  amongst  the  stars.  It  will  be  interesting,  there- 
fore, to  state  in  detail  what  those  movements  are  as  we  on  the 
Earth  see  them.  Starting  when  Mars  has  just  passed  through 
Conjunction,  it  emerges  from  the  Sun's  rays,  rising  some 
minutes  before  the  Sun,  and  having  a  direct,  that  is,  easterly 
motion  ;  but  as  this  motion  is  only  half  that  of  the  Earth  in  the 


FIGS.  93-98 


PLATE    XXVIII. 


May  12,  9^  in  spec.  (T.  E.  R.  Phillips).     April  30,  laf  in  spec.  (P.  B.  Molesworlh). 


March  31,  8|  in  spec.  (£.  M.  Antoniadi).    March  31,  6£  in  spec.  (E.  A.  L.  Attkins). 


March  31,  fij  in  spec.  (ir.  /.  //a//).       May  7,  9}  in  spec.  (T.  E.  R,  Phillips). 
Marc 


FIG.  99-100 


PLATE    XXIX. 


Sept.  20,  1909. 


Nov.  5,  1909. 

Mars  (Antoniadi). 


179 


MARS.  79 

same  direction,  Mars  appears  to  recede  from  the  Sun  in  a 
westerly  direction,  notwithstanding  that  its  true  motion 
amongst  the  stars  is  towards  the  E.  This  continues  for 
nearly  a  year,  and  ceases  when  it  has  attained  an  angular 
distance  from  the  Sun,  measured  along  the  Ecliptic,  of  about 
137°.  Then  for  a  few  days  it  does  not  seem  to  move  at  all. 
After  that  its  motion  becomes  retrograde  or  westerly  among 
the  stars,  and  so  continues  until  it  reaches  a  point  180°  from 
the  Sun,  or,  in  other  words,  is  in  Opposition  or  on  the  meridian 
at  midnight,  when  therefore  it  is  seen  at  its  best  by  us.  At 
this  time  its  retrograde  motion  amongst  the  stars  attains  its 
greatest  rapidity,  but  it  soon  slackens  and  becomes  slower  and 
slower  until  it  has  arrived  at  a  point  137°  from  the  Sun.  Then 
its  motion  again  becomes  direct  and  so  continues  till  once 
again  the  planet  is  lost  in  the  Sun's  rays,  soon  after  which  it 
reaches  Conjunction,  and  another  two-year  period  of  changes 
begins.  Though  they  are  renewed  on  the  same  principles, 
there  will  be  changes  in  the  details  ;  the  retrogradation  does 
not  always  commence  or  finish  at  137°,  for  it  may  begin  as  soon 
as  128°  is  reached,  or  may  not  begin  until  146°  is  reached, 
the  arc  described  varying  between  10°  and  19!°.  The 
duration  of  the  retrograde  motion  in  the  former  case  is  60 
days,  and  in  the  latter  80  days.  The  period  in  which  these 
changes  take  place,  at  the  interval  between  two  successive 
Conjunctions  or  two  successive  Oppositions,  constitutes  the 
synodical  period  of  780  days  already  mentioned. 

The  physical  appearance  of  Mars  as  seen  in  our  telescopes 
may  be  regarded  as  not  subject  to  much  change  except  in  one 
particular.  I  say  this  advisedly,  because  although  during  the 
past  30  years  there  has  been  a  flood  of  controversy  respect- 
ing the  appearances  presented  by  the  surface  of  Mars,  and 
there  has  been  a  great  disposition  to  indulge  in  extravagant 
language,  there  is  abundant  evidence  to  show  that  there  are 
certain  defined  marks  which  are  unchanged  and  are  probably 
unchangeable. 


80      THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

I  will  deal  with  and  dispose  first  of  all,  of  the  appearances 
which  are  mentioned  in  the  preceding  paragraph  as  being  the 
one  particular  exception  to  the  rule  of  unchangeability.  This 
statement  refers  to  the  spaces  around  the  poles,  which  are 
commonly  reputed  to  be  signs  of  the  existence  of  snow.  I 
think  this  may  be  taken  to  be  a  certainty,  because  they  are 
observed  to  diminish  when  brought  under  the  influence  of  the 
Sun  at  the  commencement  of  Mars's  summer,  and  to  increase 
again  on  the  approach  of  Mars's  winter.  The  illustrations 
annexed  are  sufficiently  self-descriptive. 

Some  anomalies  have  been  noticed  from  time  to  time  in 
regard  to  these  polar  patches,  not  sufficiently  great,  however,  I 
think,  to  negative  their  being  masses  of  snow,  but  still  somewhat 
strange.  For  instance,  whilst  both  Madler  and  Secchi  found 
the  north  patch  to  be  concentric  with  the  North  Pole  of  the 
planet,  yet  that  the  south  patch  was  not  concentric  with  the 
South  Pole.  Sir  W.  Herschel,  as  far  back  as  1784,  noticed  that 
the  patches  were -not  exactly  opposite  to  one  another. 

Spots  on  Mars  are  frequently  seen,  and  have  enabled 
astronomers  to  arrive  at  very  consistent  conclusions  as  to  the 
period  of  the  planet's  axial  rotation,  which  may  certainly  be  set 
down  at  24  hours  37  minutes. 

The  geography  (to  use  the  obviously  wrong  word)  of  the 
surface  of  Mars  has  been  attentively  studied  during  the  three 
centuries  which  have  elapsed  since  the  invention  of  the 
telescope,  and  drawings  of  every  kind,  by  astronomers  of  every 
sort,  using  telescopes  of  every  size,  exhibit  a  consistency  which 
is  very  remarkable.  No  wonder  the  whole  globe  has  been 
mapped  out  into  areas,  hypothetically  regarded  as  land  and 
water,  to  which  names,  many  of  them  very  bizarre,  have  been 
given.  The  original  series  of  names  was  restricted  in  number, 
and  included  the  names  of  some  twenty  leading  observers  of 
note  in  the  astronomical  world.  Without  saying  that  these 
names  have  been  formally  discarded,  yet  a  new  series  of 
names,  Latin  in  form  and  in  a  certain  sense  mythical,  have 


FIG.  lOOa 


PLATE  xxixa 


MARS. 
October  21,  1909  •. 


(S.  Boltoti) 


MARS.  8  r 

been  brought  into  use  and  seem  to  be  meeting  with  acceptance 
from  astronomers. 

After  the  polar  patches  spoken  of  already  the  one  most 
obvious  feature  which  most  generally  attracts  notice  when  that 
particular  hemisphere  of  Mars  where  it  is  situated  happens  to  be 
under  observation  is  that  known  as  the  "  Kaiser  Sea,"  some- 
times called  the  "  V  "  mark,  from  resemblance  to  that  letter  ; 
but  which  much  more -readily  brings  to  mind  the  continent  of 
South  America,  if  one  could  imagine  a  piece  stuck  on  at  the 
southern  tip  at  right  angles  to  the  general  trend  of  tha't  con- 
tinent. The  shape  of  a  leg  of  mutton  has  also  been  suggested. 

The  ruddy  colour  of  Mars  has  been  notorious  from  the 
earliest  times  in  which  v:ritten  mention  of  the  planet  has  been 
handed  down,  and  Sir  John  Herschel  ascribed  it  to  "  an  ochrey 
tinge  in  the  general  soil  like  what  the  red-sandstone  districts 
on  the  Earth  may  possibly  offer  to  the  inhabitants  of  Mars,  only 
more  decided."  This  idea  is  not  so  far-fetched  as  might  at 
first  be  thought. 

There  are  parishes  in  Gloucestershire,  one  of  them  named 
Red  Marley,  which,  to  those  who  have  visited  them,  would  bring 
home  Herschel's  idea.  There  might  easily  be  imparted  to  the 
Earth,  when  viewed  from  Mars,  a  very  distinct  reddish  colour 
supposing  that  there  were  many  thousands  of  square  miles  all 
geologically  resembling  the  soil  of  the  parish  of  Red  Marley. 

Another  long-standing  idea  with  respect  to  the  surface  of 
Mars  is  that  it  is  visibly  divided,  as  the  Earth  is,  into  land  and 
water,  the  ruddy  areas  being  land  and  the  almost  equally 
greenish  areas  being  water. 

The  great  controversy  of  the  present  day  respecting  Mars  is 
the  reality,  or  otherwise,  of  an  immense  number  of  "canals" 
said  to  exist  all  over  it,  and  to  show  themselves  in  the  form  of 
numerous  dark  lines,  very  straight,  and  so  well  defined  as  to 
indicate  for  them  an  artificial  origin.  The  observer  who  first 
put  forth  this  alleged  fact  and  its  explanation  has  found  a  few 
supporters,  or  men  who  have  been  claimed  as  such  because 
6 


82       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

they  thought  they  had  seen  markings  on  the  planet  which 
might  be  regarded  as  straight  lines  intercepting  one  another  at 
various  angles.  On  the  other  hand,  it  is  undoubtedly  true  that 
the  vast  majority  of  observers,  using  telescopes  of  every  size  and 
kind,  have  never  suggested  the  existence  of  any  such  precise 
markings,  or  been  able  to  find  them  when  invited  to  look  for 
them. 

Professor  W.  H.  Pickering,  taking  an 'intermediate  view,  has 
reviewed  the  controversy  respecting  the  markings  on  Mars  in 
the  following  terms  : — 

"It  has  lately  been  shown  by  Messrs.  Lane,  Maunder,  and 
Evans  that  many  of  the  finer  Martian  canals  are  probably  non- 
existent, their  appearance  being  due  to  certain  singular  optical 
illusions.  Most  of  the  broader  canals,  however,  in  the  dark 
regions  of  the  planet  undoubtedly  exist,  and  the  same  is  almost 
certainly  true  of  some  of  those  in  the  light  regions,  such  as 
Nilosyrtis  and  Nectar.  The  chief  cause  of  the  illusion  seems 
to  be  the  system  of  lakes,  or  oases,  as  they  are  sometimes 
called,  which  were  first  discovered  in  large  numbers  at 
Arequipa. 

"There  is  a  curious  tendency  of  the  human  eye  to  see  such 
dark  points  united  by  faint  narrow  lines,  and  it  has  been  shown 
by  means  of  diagrams  that  these  lines  sometimes  appear  when 
the  diagram  is  at  such  a  distance  that  the  dark  dots  are  them- 
selves invisible.  But  even  without  the  dots  the  lines  may  some- 
times appear,  joining  different  portions  of  the  dark  regions. 
We  must  therefore  divide  the  Martian  canals  into  two  classes  : 
those  that  are  genuine  and  those  that  are  not.  .  .  . 

"  This  phenomenon  of  spurious  canals  is  certainly  very 
singular,  but  we  must  IDC  careful  that  its  interest  and  unexpected- 
ness do  not  lead  us  into  the  error  of  affirming  that,  because 
many  Martian  canals  are  spurious,  therefore  all  Martian  canals 
are  imaginary.  It  seems  indeed  a  great  pity  that  so  much 
time  and  energy  should  have  been  expended  in  many  observa- 
tories in  mapping  canals  in  the  bright  regions  of  the  planet, 
and  comparatively  so  little  time  spent  on  the  darker  regions, 
where  changes  are  constantly  taking  place,  and  where  we  should 
naturally  expect  the  more  interesting  developements  to  occur." 


FIG.  101 


PLATE    XXX, 


***$«%» 


82] 


FIGS.  102-107 


PLATE    XXXI. 


[83 


MARS.  83 

At  one  time  it  was  urged  that,  not  only  was  Mars  crossed  and 
recrossed  by  sharply  defined  dark  lines,  but  that  many  of  these 
lines  were  doubled  :  hence  arose  the  word  "  germination  "  as 
applicable  to  them.  Weighing  the  pros  and  cons  of  the  con- 
troversy on  the  principles  of  the  law  of  evidence  as  applied 
by  lawyers,  I  cannot  consider  that  the  arguments  put  forth  in 
support  of  the  multiplicity  of  sharply  defined  markings  is 
established,  and  think  that  the  only  thing  which  is  established  is, 
that  there  are  numerous  markings  on  Mars  which  take  various 
shapes,  and,  when  clearly  visible,  are  at  best  ill-defined,  iand 
that  very  often  they  are  not  clearly  visible.  Finally,  that  their 
visibility  depends  in  no  small  degree  on  the  personality  of  the 
observer  and  on  atmospheric  and  other  circumstances. 

There  is  one  matter  connected  with  Mars  which  has  yet  to 
be  mentioned,  namely,  its  satellites.  Though  these  cannot 
be  said  to  concern  the  general  reader  because  of  their  diminu- 
tive size,  yet  a  certain  amount  of  historic  interest  attaches  to 
them.  They  were  only  discovered  as  recently  as  the  year 
1877,  when  an  American  observer,  A.  Hall,  conceived  the  idea 
of  turning  to  account  the  favourable  Opposition  of  that  year  to 
search  for  a  satellite,  as  he  had  at  command  the  fine  refracting 
telescope  of  the  Washington  Observatory,  carrying  an  object- 
glass  26  in,  in  diameter.  His  efforts  were  soon  rewarded  by 
the  discovery  not  only  of  one,  but  of  two  satellites,  which  have 
been  named  Phobos  and  Deimos,  the  names  of  the  steeds  said 
by  Homer  to  have  drawn  the  chariot  of  Mars. 

When  it  is  stated  that  Phobos  at  its  best  is  no  brighter  than  a 
star  of  Magnitude  1 1 ,  whilst  Deimos  is  as  faint  as  a  star  of  Magni- 
tude 13,  it  will  be  realised  at  once  that  only  telescopes  of  very 
large  size  can  observe  them.  Historically  it  is  interesting  to  note 
that,  in  Gulliver's  Travels,  the  astronomers  of  Laputa  are 
spoken  of  as  having  discovered  that  Mars  had  two  satellites, 
whilst  Voltaire,  in  his  "  Romance  of  Micromegas,"  ascribes  to 
some  of  his  characters  also  the  discovery  of  two  Martial 
satellites  "  which  had  escaped  the  scrutiny  of  our  astronomers." 


84      THE   MOST   INTERESTING   AND    FAMILIAR    PLANETS. 

It  is  to  be  presumed  that  Voltaire  was  only  a  copyist  of  Dean 
Swift. 

Mars  travels  round  the  Sun  in  686  days,  at  a  mean  distance 
of  140,000,000  miles.  The  eccentricity  of  the  orbit,  though  a 
good  deal  less  than  that  of  the  orbit  of  Venus,  is  nevertheless 
very  considerable,  so  that  the  planet's  distance  from  the_  Sun 
may  on  occasions  be  as  great  as  154,000,000  miles,  or  as  little 
as  128,000,000  miles.  The  planet's  apparent  diameter  varies 
between  4"  in  Conjunction  and  30"  in  Opposition.  Owing  to 
the  great  eccentricity  of  the  orbit  the  apparent  diameter,  as 
seen  from  the  Earth,  will  also  differ  greatly  at  different  times. 
The  real  diameter  may  be  regarded  as  almost  exactly  5000 
miles. 

JUPITER. 

On  the  whole,  Jupiter  may  be  said  to  be  the  planet  most 
easily  brought  within  the  reach  of  everybody,  and  for  this 
reason  ;  it  is  generally  visible  for  many  months  in  every  year  ; 
it  is  more  or  less  conspicuous  owing  to  its  normal  brightness, 
and,  from  the  standpoint  of  the  mere  sightseer,  its  belts  and  4 
principal  satellites  are  within  the  reach  of  quite  small  telescopes. 
Indeed,  instances  are  on  record  of  the  satellites,  when  suffi- 
ciently near  to  join  forces  as  regards  their  combined  light, 
have,  under  very  favourable  circumstances  of  atmosphere  and 
the  observer's  keenness  of  vision,  been  visible  to  the  naked  eye. 

Jupiter  is  the  largest  of  all  the  planets,  having  a 
diameter  of  about  88,000  miles.  So  large  a  body  rotating  on 
its  axis  in  the  short  time  of  10  hours  or  thereabouts,  it  follows 
that,  by  the  laws  of  rotatory  motion,  the  compression  of  the 
polar  diameter  is  very  marked,  amounting,  according  to  the 
best  authorities,  to  about  TVth  of  the  equatorial  diameter. 

The  belts  have  long  been  known  as  a  notable  feature  of  the 
planet.  There  is  a  certain  amount  of  permanency  about  them, 
yet  it  cannot  be  said  that  they  are  permanent.  To  look  at 
them,  they  are  dusky  streaks  of  different  breadths,  which 


JUPITER.  85 

breadths  vary  from  time  to  time.  Sometimes  they  chiefly 
appear  as  two  or  three  broad  belts,  at  another  time  the 
observer  will  notice  a  greater  number  of  belts,  all  much 
narrower  than  those  he  may  have  seen  on  some  previous 
occasion.  They  are  all  parallel  to  the  planet's  Equator,  though 
commonly  absent  actually  under  the  Equator.  On  very  rare 
occasions  a  single  belt  may  be  noticed  lying  askew  to  the 
general  trend  of  the  belts.  The  latest  recorded  instance  of 
this  was  in  April  1910,  S.  Bolton  being  the  observer.  It  may 
be  taken  for  granted  that  in  looking  at  Jupiter  we  are  not 
looking  at  anything  in  the  nature  of  a  solid  body,  but  only  at 
a  cloudy  envelope,  which  may  or  (more  likely)  may  not  en- 
compass a  solid  globe.  It  has  been  suggested  that  the 
changes  visible  on  Jupiter  are  proofs  of  the  manifestation  of 
energy  in  the  form  of  heat  on  the  planet. 

The  question  as  to  their  colour  sometimes  arises,  because, 
though  generally  grey  or  greyish,  distinct  tinges  of  brown  may 
be  traced,  whilst  in  1877  a  great  red  spot  burst  forth,  which 
remained  for  many  years  a  striking  and  permanent  feature. 
The  later  history  of  this  spot  is  very  remarkable,  and  there  is 
a  mystery  about  it  which  is  still  unsolved.  It  retained  its 
shape  and  colour  for  about  four  years,  up  till  the  autumn  of 
1882,  when  it  began  sensibly  to  fade  ;  and  during  the  ensuing 
year  it  became  extremely  faint,  though  still  preserving  its  form. 
In  the  years  between  1884  and  1906  it  underwent  various 
changes,  never  recovering  its  original  bright  colour.  In  1906, 
whilst  the  shape  remained,  the  tinge  of  colour  was  no  more 
than  grey,  though  something  slightly  wanner  was  sometimes 
suspected.  In  1909  the  spot  was  all  but  invisible,  though  its 
outline  could  be  detected  ;  but  it  more  than  ever  presented  the 
appearance  of  being  something  which  was  floating  in  a  basin 
or  hollow.  In  1910  it  again  became  visible,  though  only  for 
a  few  weeks,  and  now  one  can  hardly  say  more  than  that  its 
place  can  be  discovered. 

The  illustrations  annexed  will  indicate  the  fact  that  during 


86       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

the  red  spot's  visibility,  dating  from  1878,  its  original  outline 
was  oval,  and  that,  notwithstanding  the  loss  of  colour,  which 
marked  many  subsequent  years,  yet  at  times  it  seems  to  have 
closed  up  and  lost  its  oval  shape.  The  question  has  been 
mooted  whether  the  oval  spot  of  1878,  with  its  strongly  defined 
colour,  could  be  identical  with  an  elliptical  ring  which  was 
observed  and  occupied  the  same  position  in  latitude  in  1869  and 
1870,  but  which  did  not  possess  any  definite  colour.  That 
elliptical  ring  seems  to  have  disappeared  unnoticed,  but  the 
red  spot  of  1878  at  one  time  showed  signs  of  becoming  itself 
transformed  into  an  elliptical  ring  and  closing  up.  The  red 
spot,  minus  nearly  or  all  its  colour,  seems  still  to  be  visible, 
or  at  least  traceable,  but  there  is  distinct  evidence  that  it  has 
in  the  course  of  years  moved  on — that  is  to  say,  does  not 
occupy  the  same  position  in  longitude  which  it  did  when  first 
discovered,  and  for  many  years  afterwards. 

This  history,  though  very  condensed,  will  justify  the  remark 
that  there  is  something  mysterious  about  this  spot,  for  which 
no  counterpart  can  be  found  anywhere  in  the  domain  of 
astronomy.  It  remains  to  be  added  that  though  we  talk  about 
the  red  spot  as  having  been  discovered  in  1877,  there  seems 
considerable  evidence  that  a  spot  of  the  same  shape  was 
noticed  very  many  years  earlier  :  indeed,  as  far  back  as  1666, 
as  witness  the  accompanying  copy  of  an  old  sketch  (Fig.  129), 
ascribed  to  Azout  and  Cassini  jointly. 

White  spots  have  also  been  noticed  of  various  sizes  at  various 
times,  and  also  occasionally  dark  spots,  but  no  explanation  of 
the  physical  character  of  them  is  available.  We  have  evidently 
a  good  deal  to  learn  respecting  Jovian  spots,  and  several 
surmises  have  already  been  put  forward.  Whilst  it  has  been 
thought  that  some  connection  exists  between  Sun-spots  as 
regards  their  period  and  the  position  of  Jupiter  in  its  orbit,  the 
idea  has  been  extended  to  the  point  that  there  is  an  identity 
in  time  between  the  prevalence  of  spots  on  the  Sun  and  spots 
on  Jupiter.  Whether  these  spots  stand  to  one  another  as 


FIGS.  109-116 


PLATE    XXXIII. 


Jupiter's  Red  Spot  and  the  Regions  near  (Denning). 


-  861 


i  1880,  Nov.  19 
3  1881,  Dec.  7 
5  1883,  Oct.  15 
7  1885,  Feb.  25 


M. 

23 
40 
37 
50 


2  1881,  Sept.  26 
4  1882,  Oct.  30 
6  1884,  Feb.  6 
8  1885,  May  9 


H.  M. 

13  ii 

16  10 

9  29 


FIGS.  117-128 


PLATE    XXXIV. 


JUPITER. 


cause  and  effect,  or  whether  both  are  indications  of  disturbances 
of  cosmical  origin  from  outside  the  solar  system  is  a  matter 
on  which  no  opinion  can  be  pronounced  with  our  present 
limited  knowledge. 

As  regards  Jupiter's  belts  taken  collectively  it  seems  not  open 
to  doubt  that  they  exhibit  from  time  to  time  not  only  distinct 
traces  of  colour,  such  as  pale  purple,  or  brown,  or  orange,  but  that 
this  colour  varies  from  time  to  time  in  a  way  which  almost  im- 
plies that  its  greatest  developement  is  coincident  with  a  maximum 
display  of 
Sun-spots. 
This  was 
Browning's 
idea,  put 
forth  many 
years  ago  ; 
but  I  am 
not  aware 
that  any 
recent  ob- 
server has 
given  his 
attention  to 
the  matter 
from  this 
standpoint. 

The  satellites  of  Jupiter,  8  in  number,  have  two  distinct 
histories,  so  to  speak  ;  that  is  to  say,  that  the  newly  discovered 
ones  have  a  history  and  individual  characteristics  which  en- 
tirely dissociate  them  from  the  4  original  satellites,  as  they 
may  be  conveniently  termed.  The  original  4  were  discovered 
by  Galileo  in  January  1610  as  the  first-fruits  of  the  application  of 
the  telescope  to  the  observation  of  Jupiter.  A  man  named 
Simon  Marius,  who  put  in  a  claim  for  priority  over  Galileo, 
named  them  lo,  Europa,  Ganymede,  and  Callisto  ;  but  this  claim 


North 
Fig.  129. 


88       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 


was  so  universally  (but  perhaps  not  rightly)  considered  to  be 
fraudulent  that  astronomers  agreed  to  show  their  opinion  by 
ignoring  the  names  prescribed  by  Marius,  and  simply  to 
identify  the  satellites  by  their  order  of  distance  from  their 
primary,  designating  them  as  I.,  II.,  III.,  IV.  The  condition 
of  things  here  implied  remained  undisturbed  until  1892,  when 
a  distinguished  American  astronomer,  E.  E.  Barnard,  dis- 
covered a  5th  satellite,  very  much  smaller  than  all  the  others, 
revolving  round  its  primary  within  the  orbit  of  I.  Rather 
more  than  12  years  later  another  American,  Perrine,  dis- 
covered a  6th  and  a  yth  satellite,  both  revolving  outside 
IV. ;  and  in  1908  Melotte,  an  assistant  at  the  Greenwich  Ob- 
servatory, introduced  an  8th  satellite  to  the  astronomical 
world.  These  various  discoveries  can  be  most  conveniently 
exhibited  by  resort  to  a  table  as  follows : 


Designation. 

Discoverer  and  Date  of 
Discovery. 

Mean 
Distances  in 
Radii  of  4. 

Sidereal 
Period. 

d.      h. 

V. 

Barnard,  Sept.  9,  1892 

O       12 

I. 

Galileo,    Jan.     1610 

6-0 

i     18 

II. 

?5                            J»                    )  J 

9-6 

3     13 

III. 

?  J                         5  J                  >» 

i5'3 

7      4 

IV. 

5<                            »>                    1  » 

26-9 

16     18 

VI. 

Perrine,   Dec.  3,   1904 

251 

VII. 

,,         Feb.  1905  - 

265 

VIII. 

Melotte,  Feb.  28,  1908 

26  months 

All  these  new  satellites  are,  as  may  have  been  expected,  so 
very  small  as  to  be  beyond  the  reach  of  any  but  the  largest 
telescopes  in  the  world.  I  shall  therefore  here  dismiss  them, 
and  confine  my  remarks  to  the  four  old  satellites.  These  well 
deserve  the  attention  of  the  amateur  astronomer,  not  simply 
because  of  the  fact  that  they  are  easily  visible  in  the  most 
ordinary  telescopes,  but  because  they  are  incessantly  moving 


JUPITER.  89- 

about  ;  and  their  movements  give  rise  to  certain  phenomena 
called  transits  and  occupations.  A  transit  occurs  when  a 
satellite  passes  in  front  of  the  planet,  as  seen  from  the  Earth, 
and  an  occultation  when  the  satellite  passes  behind  the  planet. 
When  an  instance  of  the  former  phenomenon  appears  the 
observer  will  see,  by  careful  scrutiny,  the  satellite's  disc  and  the 
black  shadow  cast  by  the  satellite  on  the  planet.  These  two 
appearances  must  be  carefully  discriminated,  for  the  satellite 
itself  is  apt  to  escape  notice,  whilst  its  shadow  is  mistaken  for 
the  satellite  itself.  An  occultation  is,  in  its  essential  features, 
the  same  as  a  total  eclipse  of  the  sun.  In  a  total  solar  eclipse 
the  bright  body  of  the  sun  is  wholly  concealed  by  the  super- 
posed Moon.  Similarly,  in  an  occultation  of  a  Jovian  satellite 
the  bright  satellite  is  entirely  concealed  by  the  planet.  But 
there  is  this  difference  :  in  a  solar  eclipse  the  Moon,  which 
does  the  work,  is  not  only  opaque,  but  black  ;  but  in  a  Jovian 
occultation  the  occulting  body  which  does  the  work,  namely, 
the  planet,  whilst  it  is  opaque  is  nevertheless  illuminated, 
because  nothing  happens  either  to  weaken  or  put  an  end  to 
the  light  which  the  planet,  like  every  other  planet,  receives 
from  the  Sun.  These  phenomena  obtain  full  recognition  in 
the  various  national  Nautical  Almanacs,  and  the  information 
given  in  the  British  Nautical  Almanac  is  borrowed  by 
Whitaker's  Almanac,  and  so  is  brought  within  the  reach  of 
everybody,  and  no  further  amplification  of  the  subject  is 
necessary  here. 

Under  ordinary  circumstances  the  satellites  exhibit  simple 
illuminated  discs,  but  with  adequate  optical  assistance  it  is 
found  that  they  have  markings  or  shadings  of  irregular  shape. 
Comparing  one  with  another,  it  would  appear  that  III.  is 
commonly  the  brightest  and  IV.  the  faintest  ;  but  no  very 
positive  statement  can  be  made  as  to  I.  and  II.,  or  even  as 
to  the  relative  brilliancy  of  any  one  of  the  four  compared  with 
the  others,  for  it  seems  certain,  or  probable,  that  all  of  them 
are  subject  to  changes  of  brilliancy.  There  is  no  clear  evi- 


90       THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

dence  of  their  ever  showing  any  signs  of  colour.  W.-H.  Pick- 
ering has  noted  the  curious  fact  that,  twice  during  each 
revolution,  and  at  intervals  of  34  hours,  the  third  satellite 
exhibits  a  marked  elliptical  outline,  and  that  its  chief  shading 
is  not  a  band,  but  is  forked.  He  thinks  also  that  there  is 
something  abnormal  in  the  circumstances  of  II.  and  IV.  as 
distinguished  from  I. 

Observation  of  the  satellites  of  Jupiter  as  far  back  as  1675 
led  to  the  discovery  that  light  is  not  transmitted  instantaneously 
through  space,  but  takes  an  appreciable  time.  A  Danish 
astronomer,  Romer,  was  the  hero  of  this.  He  found  that  the 
observed  times  of  the  eclipses  did  not  tally  with  the  calculated 
times,  and  that  the  differences  were  systematically  affected 
by  opposite  signs  of  error,  according  as  Jupiter  was  near  to 
or  remote  from  the  Earth.  This  fact  led  him  to  suspect  that 
the  varying  differences  in  the  distances  was  the  cause  of  the 
varying  differences  in  the  times ;  in  other  words,  the  greater 
the  distance  of  the  planet  from  the  Earth  the  longer  the  time 
occupied  in  the  light  making  itself  manifest  to  us  on  the 
Earth.  Romer's  conclusions  were  that  light  travelled  at  the 
rate  of  192,000  miles  per  second,  a  conclusion  remarkably  near 
the  truth,  considering  Romer's  inferior  instruments,  for  by 
more  modern  methods,  with  altogether  superior  instruments, 
it  has  been  found  that  Romer's  figures  are  only  wrong  by 
being  about  2000  miles  in  defect,  the  true  velocity  being 
194,000  miles  per  second. 

Jupiter  revolves  round  the  Sun  in  rather  more  than  iif  years 
at  a  mean  distance  of  483,000,000  miles.  The  eccentricity  of 
its  orbit  is  small,  so  that  its  greatest  possible  and  least  possible 
distances  do  not  differ  very  much  from  its  mean  distance, 
being  506,000,000  miles  and  460,000,000  miles  respectively. 
The  planet's  apparent  diameter  varies  between  60"  in  Oppo- 
sition and  30"  in  Conjunction.  The  equatorial  diameter  is 
rather  more  than  88,000  miles,  making  Jupiter  the  largest 
planet  in  the  solar  system. 


SATURN.  9 1 


SATURN. 

There  are  probably  very  few  people  who  have  any  knowledge 
of  anything  scientific  who  have  never  heard  of  Saturn  and 
its  ring.  The  planet,  though  inferior  in  lustre  to  Mars  and 
Jupiter,  is  always  to  be  found  without  difficulty  when  in  a  dark 
sky,  shining,  as  it  does,  like  a  star  of  the  second  or  third 
Magnitude.  It  compares,  however,  unfavourably  with  its  rivals 
because  it  has  a  dull,  leaden  hue. 

Though  its  appendage  is  often  spoken  of  as  "the  Ring," 
using  the  word  in  the  singular  number,  yet  it  is  really  a  system 
of  rings  which  surrounds  the  planet,  and  the  number  grows 
with  the  size  of  the  telescope  used  to  scrutinise  it.  Whilst  a 
small  telescope  will  only  show  one  ring,  a  larger  one  will 
show  this  one  divided  into  two  ;  a  still  larger  one  will  show 
the  outermost  of  the  two  again  divided  into  two.  In  addition 
to  these  there  is  a  third  main  ring,  which  is  the  innermost  of  all. 
Unlike  the  rings  just  spoken  of,  this  innermost  ring  is  not 
bright,  but  dusky ;  and  the  name  originally  given  to  it  on  its 
discovery,  rather  more  than  half  a  century  ago,  of  the  "  crape 
ring,"  has  not  quite  fallen  into  disuse,  and  is  not  altogether 
inappropriate. 

The  history  of  the  discovery  of  this  ring  is  rather  curious, 
and  suggests  a  mysterious  origin  and  developement  of  it.  In 
1838  a  distinguished  German  astronomer,  J.  G.  Galle,  pub- 
lished an  observation  in  which  he  said  he  had  noticed  a 
shading-off  of  the  innermost  bright  ring  towards  the  planet. 
His  remark  seems  not  to  have  attracted  any  particular  notice 
until  1850,  when  G.  P.  Bond  in  America,  and  Dawes  in  Eng- 
land, independently  discovered  the  dusky  ring,  and  recognised 
it  distinctly  to  be  a  ring,  but  transparent  in  so  far  that  the  body 
of  the  planet  could  be  seen  through  it. 

This  dusky  ring  is  now  a  recognised  feature  of  Saturn,  and 
it  would  seem  to  be  wider  and  more  easily  visible  than  for- 


92        THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

merly,  and  a  division  of  the  dusky  ring  into  two  rings  has  been 
suspected.  The  germs  of  its  discovery  are  to  be  seen  in  Galle's 
note  of  1838  ;  whence,  perhaps,  it  is  permissible  to  suggest  that 
the  ring  has  gone  through  stages  of  developement  during  the 
last  three-quarters  of  a  century.  There  is  no  trace  in  the 
writings  of  either  of  the  Herschels  of  their  having  detected  any 
traces  of  a  ring  inside  the  innermost  bright  one,  though  it  must 
be  confessed  that  Picard  in  1673,  an<^  Hadley  in  1723,  saw 
something  which  might  perchance  be  identifiable  with  the  dusky 
ring  of  the  observers  of  the  igth  century. 

Saturn  and  its  system,  treated  as  a  whole,  is  not  only  a  very 
remarkable  and  interesting  object,  regarded  as  a  spectacle,  but 
every  30  years  undergoes  interesting  transformations  which 
must  now  be  described.  For  convenience  of  reference  it  is 
customary  to  call  the  outermost  bright  ring  A,  the  innermost 
bright  ring  B,  and  the  dusky  ring  C. 

Figs.  136-137  show  the  interior  edge  of  the  crape  ring  as 
drawn  in  March  1888  by  J.  G.  E.  Elger.  The  irregularities 
are  very  noteworthy,  but  I  am  not  aware  that  they  have  ever 
been  confirmed  ;  at  any  rate,  in  anything  like  the  form 
suggested  by  Elger. 

Though  under  ordinary  circumstances — that  is  to  say,  during 
a  considerable  succession  of  years— we  see  Saturn  as  a  ball 
surrounded  by  its  rings,  yet,  owing  to  the  orbit  of  Saturn  being 
inclined  to  the  plane  of  the  Ecliptic,  we  see  the  rings  at  inter- 
vals either  opened  out  very  wide  or  not  opened  out  at  all,  but 
presented  edgeways. 

Perhaps  this  will  be  made  a  little  more  clear  by  giving  some 
dates.  In  1907  the  Earth  was  in  the  plane  of  the  rings  ;  they 
were  more  or  less  invisible  for  a  short  time  (October  1907 — 
January  1908),  being  placed  edgeways  to  the  view  of  us  on  the 
Earth.  In  1907  the  Sun  began  to  illuminate  the  southern  side 
of  the  rings,  after  having  for  14!  years  shone  upon  the  northern 
side.  After  1907  the  planet  moved  on,  the  rings  beginning  to 
open  out  and  become  wider  every  year  until  1915,  when  they 


FIGS,  130-132 


PLATE    XXXV. 


Feb.  1887  (Terby). 
Saturn. 


FIGS.  133-135 


PLATE    XXXVI, 


July  30,  1899  (Antoniadi). 


Jan.  27,  1912  (Phillips). 

Saturn. 


[93 


SATURN. 


will  attain  their  maximum  breadth.     After  that  they  will  again, 
to  our  vision,  become  narrower. 

When  1922  is  reached  the  planet  will  have  accomplished  one- 
half  (approximately)  of  a  revolution  round  the  Sun,  and  will 
again  have  reached  the  condition  of  being  seen  edgeways,  the 
sun  beginning  to  illuminate  the  northern  side  of  the  rings. 
For  the  previous  14!  years  we  shall  have  seen  one  and  the 
same  side  of  the  rings,  but  henceforth  for  14!  years  to  come 
we  shall  see,  also  continuously,  for  that  period  the  same  side  of 


Fig.  136.     Ring  C,  March  21, 
1887. 


Fig.  137.-  Ring  C,  March  27, 
1887. 


the  rings  :  but  it  will  be  the  opposite  side  to  what  we  had  seen 
previously,  because  now  the  planet  with  its  rings  will  have 
passed  to  the  opposite  side  of  the  Ecliptic. 

Continuing  our  predictions,  on  or  about  1928  the  rings  will 
again  have  attained  their  maximum  opening,  but  we  shall  see, 
of  course,  the  opposite  side  of  them  to  what  we  saw  in  1914. 
Continuing  our  calendar  of  changes,  the  rings  will,  about  1936, 
reach  the  same  stage  identically  as  had  been  reached  in  1907  ; 
that  is  to  say,  the  planet  will  have  completed  one  entire  circuit 
of  the  Sun,  and  will  start  again  on  precisely  the  same  sue- 


94      THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

cession  of  changes  as  that  with  which  it  had  commenced  in 
1907,  the  Sun  beginning  again  to  illuminate  the  southern  side 
of  the  rings. 

From  the  foregoing  it  will  be  clear  that  from  now,  and  for 
several  years  after  the  first  publication  of  this  book,  the  planet 
will  be  at  its  best  for  observation  in  telescopes  of  all  sizes. 

The  changes  which  have  just  been  sketched  out  involve, 
both  theoretically  and  practically,  many  incidental  details  too 
numerous  to  be  gone  into  here  ;  but  the  reader  will  no  doubt 
understand  that,  as  we  are  dealing  not  with  a  ring  all  in  one 
piece,  but  with  a  bundle  of  rings,  so  to  speak,  the  effects  are 
somewhat  complicated.  One  of  the  most  natural  effects  is  that, 
when  the  edgeways  stage  is  nearly  reached,  or  just  passed, 
instead  of  the  edge  being  a  continuous  line  of  light,  it  is  a 
broken  line.  The  diagrams  annexed  will  make  this  sufficiently 
clear  without  any  detailed  explanation. 

The  outer  edge  of  the  outer  ring  is  visible  throughout,  but 
with  extreme  difficulty  when  standing  by  itself  as  between  b 
and  c  and  f  and  g,  and  towards  a  and  h  •  but  the  brighter 
portions  from  c  to  d  and  from  e  to  f  indicate  that  the  light  of 
the  outer  ring  is  reinforced  by  that  reflected  by  the  inner  edge 
of  the  inner  ring.  The  bright  knots  at  b  and  g  represent  the 
light  of  the  outer  ring  strengthened  by  the  concurrent  reflection 
from  the  inner  edge  of  the  outer  ring,  and  the  outer  edge  of 
the  inner  ring,  which  last-named  reaches  us  through  the  inter- 
space between  the  two  main  rings,  which  is  often  called  the 
Cassini  Division,  from  the  name  of  its  discoverer,  J.  D.  Cassini. 

One  curious  fact  seems  well  established,  namely,  that  the 
rings  are  not  concentric  with  the  ball.  This  is  a  peculiarity 
which  one  would  not  naturally  have  expected,  but  it  has  been 
shown  mathematically  to  be  essential  to  the  stability  of  the 
ring  system  ;  and  if  this  feature  did  not  exist,  and  if  the  rings 
did  not  revolve  round  the  planet,  they  would  collapse  on  to  the 
planet.  Thus  expressed,  the  statement  suggests  that  the  rings 
are  solid,  but  it  is  generally  considered  that  such  is  not  the  case  ; 


SATURN. 


95 


on  the  contrary,  that  they  are  made  up  of  myriads  of  discrete 
particles  of  matter,  so  closely  compacted  together  that  to  our  re- 
mote eyes  they  appear  as  a  solid  mass.  Considered  as  a  system 
the  rings  are  sensibly  more  luminous  than  the  planet,  and  B  is 
brighter  than  A,  B  itself  being  least  bright  at  its  inner  edge. 

Measurements  and  opinions  vary  as  to  the  thickness  of  the 
rings.  Sir  J.  Herschel  thought  that  250  miles  would  be  an 
outside  limit  for  the  thickness  ;  G.  P.  Bond  put  it  at  no  more 


Fig.  138.— Saturn,  Feb.  7,  1890. 

Photographed  at  Mount  Wilson,  U.S. 

than  40  miles ;  probably  100  miles  is  near  the  mark.  The 
general  dimensions  may  be  exhibited  in  the  following  table, 
which  represents  the  latest  and  best  measures  obtainable,  being 
those  of  Prof.  E.  E.  Barnard,  put  forth  in  1895. 

Miles. 

Outer  diameter  of  outer  ring  ....  172,310 

Inner  diameter  of  outer  ring  ....  150,560 

Outer  diameter  of  inner  ring  ....  146,020 

Inner  diameter  of  inner  ring  ....  110,200 

Inner  diameter  of  crape  ring  ....  88, 190 

Width  of  the  Cassini  division  ....  2,270 


96      THE    MOST    INTERESTING    AND    FAMILIAR    PLANETS. 

To  the  foregoing  may  be  added,  from  another  source,  18,640 
miles  as  the  distance  of  the  ring  B  from  the  ball. 

Thus  far  I  have  said  nothing  about  the  physical  appear- 
ance of  the  ball.  It  has  certain  features  in  common  with 
Jupiter— that  is  to  say,  faint  belts  may  often  be  seen 
upon  it,  and  occasionally  a  bright  spot  ;  but  these  are  very 
rare. 

Taking  the  planet  as  a  whole,  it  was  suggested  by  Lassell 
that  the  South  Pole  is  generally  darker  and  more  bluish  in 
tinge  than  the  North  Pole.  The  general  hue  of  the  planet  is 
yellowish-white,  which  to  the  naked  eye  is  commonly  regarded 
as  dull  grey — a  seeming  contradiction.  There  exists  no 
clear  evidence  that  Saturn  has  an  atmosphere  in  the  usual 
sense  of  the  term,  though  its  existence  seems  probable,  from 
the  central  portions  being  brighter  than  the  circumference. 
Theoretically  it  should  exhibit  in  Quadrature  a  slight  phase, 
but  it  must  be  so  small  that  no  wonder  none  has  ever  been 
noticed. 

Saturn  is  attended  by  satellites,  10  in  all,  of  such  diverse 
sizes  that  they  furnish  excellent  tests  for  telescopes.  The 
largest  is  that  known  as  Titan,  which  is  supposed  to  be  about 
2700  miles  in  diameter.  All  the  satellites  have  received 
name.s,  and  those  which  come  next  in  order  of  visibility  are 
lapetus,  Rhea,  Dione,  Tethys,  and  Enceladus.  Telescopes  of 
the  largest  size  are  required  to  show  Mimas,  Hyperion,  Phoebe, 
and  Themis.  It  is  obvious,  from  the  foregoing  statement,  that, 
with  the  exception  of  Titan  and  lapetus,  amateur  observers 
will  not  need  to  give  much  attention  to  these  satellites.  Titan 
may  be  compared  to  a  star  of  Mag.  8  and  lapetus  to  one  of 
Mag.  9 ;  but  lapetus  is  generally  considered  to  vary  in 
brightness,  being  brightest  when  in  the  western  part  of  its 
orbit. 

Saturn  revolves  round  the  Sun  in  29^  years  at  a  mean 
distance  of  886,000,000  miles,  in  an  orbit  slightly  eccentric. 
Its  apparent  diameter  varies  between  1 5"  in  Conjunction  and  20" 


SATURN.  97 

in  Opposition.  According  to  Barnard,  its  equatorial  diameter 
is  76,470  miles,  and  its  polar  diameter  69,770,  which  figures 
imply  a  polar  compression  of  ^.  This  result  is  not  altogether 
in  accordance  with  the  results  of  previous  measures  which 
have  made  the  compression  more  considerable.  Hind  put  it 
as  much  as  i. 


CHAPTER   VII. 
THE  LESS  KNOWN  PLANETS* 

The  Planets  of  this  chapter  of  little  interest  to  the  amateur. — History  of 
the  discovery  of  Uranus. — Difficulties  as  to  its  orbit. — Siispicions  of 
the  orbit  being  disturbed  bv  another  planet. — The  search  for  it. — 
The  researches  of  Adams  and  Leverrier. — The  discovery  of  Neptune. — 
Brief  description  of  the  planet. — 7/5  one  satellite. — The  Minor 
Planets. — First  organised  search  for  them. — Early  discoveries. — 
Recent  discoveries  facilitated  by  photography.  —  The  planets  now 
very  numerous. — And  few  of  them  of  any  interest. — Their  fantastic 
names. — Some  particulars  of  the  first  four. — Summary  respecting 
their  orbits. 

THE  planets  which  will  come  under  our  notice  in  this  chapter 
are  of  no  intrinsic  interest  whatever  to  the  amateur  star-gazer, 
who,  if  he  tried  to  find  them,  would  in  general  have  great 
difficulty  in  doing  so  ;  and,  having  found  half  a  dozen  of  the 
brightest  of  them,  which  perhaps  he  might  do,  he  would  very 
quickly  come  to  the  conclusion  that  they  were  not  worth  the 
search.  In  spite  of  this,  however,  certain  of  them  have  great 
historic  interest,  the  tale  of  which  must  now  be. unfolded. 

On  the  evening  of  March  13,  1781,  Sir  W.  (then  Mr.)  Herschel 
was  examining  some  small  stars  near  H  Geminorum,  and  one 
of  them  attracted  his  special  attention.  With  a  view  of  seeing 
what  he  could  make  of  it  with  a  stronger  eye-piece,  he  replaced 
the  eye-piece  which  he  had  been  using  by  one  of  greater 
power. 

A  star  thus  examined  by  the  use  of  different  eye-pieces  always 
retains  its  stellar  character  of  rays  emanating  from  a  point ;  but 

98 


URANUS.  99 

Herschel  found  that  the  object  which  he  had  under  view  did 
not  behave  thus,  but  that  increasing  the  power  increased  the 
diameter  considerably,  thus  proving  that,  whatever  the  object 
was,  it  was  at  any  rate  not  a  star.  Apparently  no  suspicion 
entered  his  head  that  he  was  looking  at  a  new  planet,  for  the 
idea  of  there  being  any  new  planets  never,  up  to  that  time, 
seems  to  have  entered  seriously  into  anybody's  head. 

Finding  that  the  object  was  in  motion  amongst  the  stars,  he 
jumped  at  the  conclusion  that  he  had  found  a  new  Comet, 
and  he  announced  it  as  such  to  the  Royal  Society  on  April  26. 
But  previously  to  this,  as  early  as  March  17,  the  stranger 
had  been  examined  by  Maskelyne,  the  Astronomer  Royal,  at 
Herschel's  instigation.  Maskelyne  seems  to  have  suspected 
the  planetary  nature  of  the  new  body  almost  from  the  first. 
Notice  of  the  discovery  of  something  having  been  made  public 
the  stranger  was  observed  at  various  European  observatories 
for  many  weeks,  still  treated  as  a  comet. 

When  its  movements  were  subjected  to  calculation  on  the 
supposition  that  it  was  a  comet,  and,  like  most  comets,  one 
moving  in  a  parabolic  orbit,  it  was  soon  found  that  this  sup- 
position broke  down,  its  course,  on  the  parabolic  theory,  being 
falsified  more  and  more  as  the  observations  were  prolonged. 

The  final  stage  in  the  researches  as  to  the  real  nature  of  the 
newly  discovered  visitor  were  reached  when  Lexell  authorita- 
tively announced  that  the  object  which  astronomers  had  been 
following  was  not  a  comet  but  a  planet,  hitherto  unknown, 
revolving  round  the  Sun  in  a  nearly  circular  orbit. 

This  announcement  came  as  a  shock,  in  a  certain  sense,  to 
many  people,  because  it  seems  to  have  been  thought  that  the 
number  of  the  moving  luminaries  visible  to  the  naked  eye, 
recognised  as  7  from  the  earliest  ages,1  was  a  perfect  number 
which  it  was  almost  an  outrage  to  challenge.  A  long  controversy, 
which  was  not  really  finally  closed  till  the  middle  of  the 

1  The  Sun,  Mercury,  Venus,  the  Earth,  Mars,  Jupiter,  Saturn.    The  Sun  was 
always,  in  early  times,  considered  a  moving  body. 


100  THE    LESS    KNOWN    PLANETS 

i  gth  century,  arose  as  to  the  name  to  be  given  to  the  new 
planet.  Herschel,  in  pursuance  of  the  fashion  of  the  times, 
proposed  to  call  it  the  "  Georgium  Sidus,"a  suggestion  naturally 
not  very  acceptable  to  foreigners,  nor  indeed  very  reasonable. 
The  French  proposal,  put  forth  either  by  Lalande  or  Laplace, 
to  call  it "  Herschel"  was  equally  irrational ;  and,  finally,  there  was 
a  large  preponderance  of  opinion  in  favour  of  a  mythological 
name  which  would  harmonise  in  some  sense  with  the  name  of 
the  next  nearest  planet,  Saturn.  Agreement  thus  far  did  not 
immediately  settle  the  matter,  and  Neptune,  Astraea,  Cybele,  and 
Uranus  all  had  their  supporters.  Finally,  however,  the  last  of 
these  names,  urged  by  Bode,  gained  the  day. 

The  conservatism  of  the  English  mind  even  in  things 
astronomical  was  shown  by  the  fact  that  the  names  "Herschel " 
and  "  Georgium  Sidus  "  in  one  shape  or  other  were  kept  up  for 
a  very  long  time  in  England,  and  the  word  "  Georgian "  did 
not  disappear  from  the  Nautical  Almanac  until  the  volume 
for  1850  published  in  1846.  The  actual  name  used  for  many 
years  had  been  in  the  English  form,  "  The  Georgian,"  instead  of 
Georgium  Sidus,  which  only  lasted  a  very  few  years  after  1781. 

The  question,  Did  anybody  catch  sight  of  Uranus  before 
Herschel  ?  naturally  suggested  itself  to  astronomers  ;  and  search 
amongst  old  records  of  observations  of  stars  eventually  led 
to  it  being  ascertained  that  the  planet  had  been  observed 
on  20  occasions  between  1690  and  1771  ;  by  Le  iMonnier, 
in  particular,  on  no  less  than  12  occasions.  Had  this 
astronomer  possessed  a  methodical,  orderly  mind  it  seems 
almost  certain  that  he  could  have  anticipated  Herschel  in 
determining  the  planetary  nature  of  the  "  star  "  so  many  times 
seen  by  him  ;  but  he  was  not  a  man  of  an  orderly  mind,  if  we 
may  rely  upon  Arago's  statement  that  he  had  once  been 
shown  by  Bouvard  one  of  Le  Monnier's  observations  of  the 
planet  written  on  a  perfumer's  hair-powder  paper-bag. 

The  physical  appearance  of  Uranus,  owing  to  its  great 
distance  from  us,  and  small  apparent  size  at  its  best,  need  not 


•JRANTJS.  -  10 1 

detain  us.  Suffice  it  to  say,  therefore,  that  belts  and  spots  on 
it  have  been  suspected  by  observers  with  telescopes  sufficiently 
powerful  to  grapple  with  it.  It  has  also  been  thought  to  have 
some  inherent  light  of  its  own  besides  what  it  derives  from  the 
Sun. 

Sir  W.  Herschel  thought  he  had  discovered  6  satellites  as 
belonging  to  Uranus,  but  it  is  now  recognised  that  only  two  of 
these  were  genuine  discoveries.  Two  other  satellites  were  found 
in  1847  by  Lassell  and  O.  Struve  respectively,  and  the  assured 
number  stands  at  present  only  at  4.  They  have  been  named 
Ariel,  Umbriel,  Titania,  and  Oberon,  in  the  order  of  distance 
from  the  planet,  reckoning  outwards. 

Uranus  revolves  round  the  Sun  in  rather  more  than  84  years 
at  a  mean  distance  of  1,781,000,000  miles.  The  orbit  is  some- 
what less  eccentric  than  that  of  Jupiter.  Its  apparent  diameter 
varies  but  slightly,  and  may  be  taken  at  something  under  4",  the 
real  diameter  being  about  31,000  miles.  One  of  the  difficulties 
which  had  to  be  solved  in  connection  with  Uranus  was  the 
choice  of  a  symbol  for  it.  The  one  in  use  is  a  composite  affair 
embracing  a  capital  H,  the  initial  of  HerschePs  surname  ;  but 
the  Germans  employ  one  "  made  in  Germany "  which 
does  not  differ  much  from  the  symbol  in  common  use  for 
Mars. 

The  next  section  will  bring  the  name  of  Uranus  before  us 
again  in  a  very  striking  connection. 

NEPTUNE. 

The  story  of  the  discovery  of  the  planet  Neptune  has  often 
been  told,  but  it  will  bear  repetition  ;  at  any  rate,  this  volume 
would  not  be  complete  without  the  story  being  told  again,  even 
if  only  in  a  concise  form.  It  involves,  indeed,  the  history  of 
Uranus,  some  part  of  which  must  be  given  as  a  preface  to  the 
story  of  Neptune.  It  has  already  been  stated  that  Uranus  had 
been  observed  on  numerous  occasions  before  the  official  date  of 


102  THE   LESS    KNOWN    PLANETS. 

its  discovery  by  W.  Herschel,  and  that  these  observations 
began  as  far  back  as  1690. 

It  is  the  practice  of  astronomers,  in  calculating  the  orbit  of  a 
new  planet  or  comet,  to  base  their  calculations  on  as  long  a 
chain  of  observations  as  possible,  and  from  the  undoubted  fact 
that  when  they  began  to  calculate  the  path  of  Uranus  round  the 
Sun  they  were  able  to  start  their  chain  from  as  early  a  date 
as  1690,  they  had  great  hopes  that  very  trustworthy  details  of 
the  orbit  would  soon  be  evolved.  The  man  who  took  this 
matter  in  hand  was  the  French  astronomer,  Alexis  Bouvard. 

Bouvard,  who  in  1821  produced  his  first  detailed  results, 
was  obliged  to  confess  that  those  results  were  very  unsatis- 
factory, in  so  far  that  those  which  depended  upon  the  careful 
observations  made  in  1781-1820  would  not  harmonise  with  those 
made  during  the  91  years  prior  to  1781.  He  thought  only  of 
one  way  of  getting  over  the  difficulty,  and  that  was  by  the 
summary  process  of  rejecting  all  the  earlier  observations  as 
worthless. 

For  a  while  this  seemed  to  remove  all  difficulties,  and  the 
conclusions  from  theory  published  in  1821  and  based  on  the 
then  recent  observations,  appeared  to  fit  in  quite  satisfactorily 
with  the  observations  then  being  made.  But  this  happy  state 
of  things  only  lasted  a  few  years.  Discordancies  soon  appeared 
between  the  places  which  ought  to  have  been  occupied  in  the 
heavens  by  Uranus  according  to  Bouvard's  theory  of  the 
character  of  its  orbit  and  the  places  in  which,  by  observation, 
the  planet  was  actually  found.  It  seemed  to  be  affected  by 
some  influence  which  at  one  time  pushed  it  forwards  and  at 
another  time  pulled  it  backwards  in  its  orbit. 

It  gradually  became  certain  that  there  was  some  cause  at 
work  which  disturbed  the  planet's  movements,  and  the  con- 
clusion was  eventually  arrived  at  that  the  cause  was  some 
unknown  planet  revolving  round  the  Sun  in  an  orbit  outside 
that  of  Uranus.  An  English  amateur,  the  Rev.  T.  Hussey, 
seems  to  have  been  the  first  to  have  put  forward  this  idea  in 


NEPTUNE.  103 

a  positive  form,  which  he  did  to  Professor  G.  B.  Airy,  the 
Astronomer  Royal,  but  who  had  been  Professor  of  Astronomy 
in  the  University  of  Cambridge. 

Other  astronomers  accepted  the  idea,  but  the  first  to  take 
overt  action  was  a  young  Cambridge  Undergraduate,  J.  C.  Adams, 
who  as  early  as  1841  made  up  his  mind  to  investigate  the 
question.  Lack  of  time  prevented  him  seriously  starting  his 
labours  until  1843.  He  carried  them  on  for  if  years  on  the 
supposition  that  there  really  was  an  undiscovered  planet,  and 
in  October  1845  he  forwarded  to  Airy  provisional  elements  of 
the  orbit  and  probable  mass  of  a  planet  which  would  explain 
the  irregularities  in  the  movements  of  Uranus.  This,  on  the 
theoretical  side  of  the  question,  was  the  settlement  of  the 
question,  but,  most  unfortunately  for  the  credit  both  of  Adams 
and  Airy,  the  latter  ignored  at  the  time  the  young  Cambridge 
student  and  his  labours  and  conclusions. 

The  scene  now  changes  for  a  time  to  France.  In  the  summer 
of  1845  a  young  Frenchman,  U.  J.  J.  Le  Verrier,  of  Paris,  took 
up  the  question  of  the  anomalous  movements  of  Uranus,  and  in 
November  of  that  year  published  his  first  Essay  to  show  what 
was  not  the  cause  disturbing  the  orbit  of  Uranus.  A  few 
months  afterwards,  namely  in  June  1846,  he  published  a  second 
Essay,  in  which  he  showed  what  was  the  cause,  namely,  the 
attraction  exercised  by  an  unknown  planet.  He  assigned 
elements  to  it,  just  as  Adams  had  done  8  months  previously. 

A  copy  of  this  second  Essay  reached  Airy  on  June  23,  and 
when  he  found  how  close  was  the  accord  both  between  the  sug- 
gested elements  and  the  suggested  position  of  the  planet  in  the 
heavens,  as  assigned  by  the  two  young  mathematicians  working 
in  ignorance  of  one  another,  it  at  last  dawned  upon  him  that 
perhaps  Adams's  labours  were  not  so  unworthy  of  consideration 
as  apparently  he  had  thought  when  they  first  came  into  his 
possession  many  months  previously.  Impressed  for  the  first 
time,  he  communicated  with  Professor  Challis,  at  Cambridge, 
who  had  the  command  of  a  large  telescope  suitable  for  hunting 


104  THE    LESS    KNOWN    PLANETS. 

up  the  planet,  and  Challis  began  his  search  on  July  i  ;  but  he 
was  confronted  by  one  serious  difficulty  :  he  possessed  no  star- 
map  of  the  particular  part  of  the  heavens  in  which  it  might  be 
expected  that  the  planet  would  be  found.  He  therefore  had  to 
make  a  map  for  himself,  and  this  of  course  was  a  time-taking 
matter  which  hindered  rapid  progress.  However,  he  eventually 
prepared  the  necessary  chart,  and  when  it  was  ready  he  set  to 
work  to  use  it  ;  but  it  was  not  until  September  29  that  he  found 
an  object  whose  appearance  attracted  his  attention.  This 
subsequently  proved  to  be  the  planet  he  was  searching  for. 

Further  consideration  showed  that  he  had  observed  it, 
regarding  it  as  a  star,  on  August  4  and  12,  and  that  the  sup- 
posed star  of  August  12,  was  missing  from  the  chart  of 
July  30. 

Meanwhile,  still  in  ignorance  of  what  was  going  on  in 
England,  Le  Verrier  published  in  August  a  third  Essay  assign- 
ing more  positively  the  probable  position  of  the  planet  in  the 
heavens.  He  sent  a  summary  of  this  revised  information  to 
Encke,  the  Director  of  the  Berlin  Observatory,  and  invited  him 
to  examine  the  heavens  in  and  near  the  predicted  place. 
Encke,  fortunately,  had  just  become  possessed  of  a  newly 
published  map  of  the  locality  where  the  planet  was  expected 
to  be  found,  and  therefore  he  was  not  called  upon  to  waste 
time  in  making  a  map  for  himself,  as  Challis  had  been  obliged 
to  do. 

Encke  had  with  him  two  young  assistants,  whose  names 
afterwards  became  famous  in  the  astronomical  world,  J.  G.  Galle 
and  H.  L.  D'Arrest.  These  men,  under  Encke's  directions,  set 
to  work  the  same  night  that  Le  Verrier's  letter  arrived,  Galle 
calling  out  one  by  one  the  stars  visible  in  the  telescope,  whilst 
D'Arrest  checked  the  map.  This  work  had  gone  on  for  a 
certain  time  when  Galle  found  what  seemed  to  be  an  8th  mag. 
star  which  was  not  marked  on  the  map.  It  was  seen  again  on 
September  24,  and,  having  moved,  was  soon  proved  to  be  the 
planet  wanted.  An  examination  of  the  dates  just  given  will 


NEPTUNE.  105 

make  it  quite  clear  that  the  honour  of  the  discovery  was  shared 
in  fairly  even  proportions  by  England  and  France. 

Adams  and  Le  Verrier  both  assigned  a  position  for  the 
planet  which  proved  to  be  nearly  true  and  substantially 
identical  (with  a  slight  preponderance  in  favour  of  Le  Verrier), 
whilst  Challis  was  the  first  to  find  the  planet,  and  Galle  the 
first  to  recognise  that  the  object  seen  was  the  planet.  It 
should  be  added  that  it  was  not  until  October  i,  two  days  after 
he  had  suspected  that  he  had  found  the  planet,  that  Challis 
became  aware  of  Galle's  definite  conclusion  arrived  at  six  days 
previously.  In  the  language  of  the  gamester,  we  may  with 
perfect  accuracy  say  "honours  divided." 

It  was  a  long  time  (many  years,  in  fact)  before  French  men 
of  science  settled  down  philosophically  to  accept  the  verdict, 
which  may  now,  however,  be  regarded  as  the  verdict  of  the 
world,  though  even  to  this  day  one  may  find  French  writers 
glossing  over  or  suppressing  Adams's  name  in  connection  with 
Neptune's  discovery. 

The  remarkable  feature  about  it  was  that  two  men  of 
different  nationalities,  working  in  different  ways,  with  different 
materials,  each  unknown  to  the  other,  should  have  fixed  the 
position  in  the  heavens  of  a  planet  which  nobody  had  ever 
seen,  accurately  within  2^°  in  Adams's  case,  and  within  about  i° 
in  Le  Verrier's  case.  I  may  well  end  my  statement  of  the 
matter  in  the  words  of  Hind  : — 

"  Such  is  a  brief  history  of  this  most  brilliant  discovery,  the 
grandest  of  which  astronomy  can  boast,  and  one  that  is  destined 
to  a  perpetual  record  in  the  annals  of  science— an  astonishing 
proof  of  the  power  of  the  human  intellect." 

After  much  discussion  "  Neptune  "  was  the  name  agreed 
upon  for  the  new  planet.  Galle  suggested  "Janus,"  but  this 
name  was  disapproved  of  as  too  suggestive  of  the  idea  that  the 
orbit  of  Neptune  marked  the  entrance  into  the  solar  system 
from  outside.  And  perhaps  it  was  well  that  this  suggested 


106  THE    LESS   KNOWN   PLANETS. 

alternative  name  was  rejected,  now  that  we  seem  drifting  into 
the  belief  that  there  is  yet  another  planet  farther  off  than 
Neptune  waiting  to  be  discovered. 

Information  is  sadly  lacking  as  to  the  physical  appearance  of 
Neptune,  owing  to  its  immense  distance  and  small  apparent 
size.  Markings  in  the  nature  of  belts,  and  even  a  ring,  have 
been  hinted  at  by  several  observers ;  but  it  may  be  said  that 
practically  we  know  nothing  on  the  subject.  If  a  ring  existed 
it  would  only  open  out  every  82  years,  being  the  point  of  a  semi- 
revolution  round  the  Sun  ;  so  it  might  be  many  years  yet  before 
its  existence  could  be  certainly  known. 

The  existence  of  one  satellite  seems  to  be  assured,  and  a 
second  has  been  suspected,  but  here  again  there  is  a  great  lack 
of  assured  knowledge,  and  it  is  not  a  little  surprising  that,  with 
the  large  telescopes  lately  brought  into  use,  especially  in 
America,  so  little  attention  should  have  been  given  to  Neptune. 

Neptune  revolves  round  the  sun  in  164  years  at  a  mean 
distance  of  2,791,000,000  miles.  The  eccentricity  of  the  orbit  is 
small.  The  planet's  apparent  diameter  only  varies  between 
2'6"  and  2*8".  Its  true  diameter  is  about  37,000  miles. 

THE   MINOR   PLANETS 

The  discovery  of  the  planet  Uranus  had  other  after-influences 
besides  leading  to  the  discovery  of  Neptune.  The  fact  that  the 
ancient  tradition  of  seven  moving  heavenly  bodies,  and  no  more, 
had  been  broken  in  upon  put  it  into  the  minds  of  certain 
astronomers  that,  as  there  was  an  eighth  planet  (Sun  and  Moon 
having  anciently  been  treated  as  planets),  namely  Uranus,  why 
not  others  ? 

The  actual  circumstances  which  gave  a  practical  start  to  the 
idea  that  there  were  more  planets  to  be  found  if  they  were 
looked  for  are  rather  curious.  A  certain  J.  D.Titius,  of  Wit- 
temberg,  in  Germany,  discovered  the  following  curious 
coincidences. 


THE    MINOR    PLANETS. 


107 


Take  the  numbers  o,  3,  6,  12,  24,  48,  96,  192,  384,  each  of 
which  after  the  3  is  double  its  predecessor  ;  add  4  to  each 
number  and  we  get  4,  7,  10,  16,  28,  52,  100,  196,  388. 

Now  these  numbers  approximately  represent  the  distances  of 
the  planets  from  the  Sun,  taking  the  Earth's  distance  as  the  unit 
or  standard,  calling  it  10. 

This  statement  will  be  more  clear  if  it  is  tabulated  thus  : 


Planets. 


Mercury         . 

Venus    .         ... 

Earth    . 

Mars 

[Ceres,  not  known  in  1772]   . 

Jupiter 

Saturn 

[Uranus,  not  known  in  1772] 
[Neptune,  not  known  in  1772] 


True  distance 

from  Q. 

Distance  by 
Bode's  Law. 

3'*7 

4'00 

7-23 

7-00 

lO'OO 

lO'OO 

!5'23 

1  6-00 

[27-66] 

28-00 

52-03 

52-00 

95-39 

lOO'OO 

[191-83] 

196-00 

[300-37] 

388-00 

Another  German  astronomer,  J.  E.  Bode,  became  acquainted 
with  Titius's  figures,  and,  adopting  the  idea  as  his  own,  and 
noticing  at  that  time  (1772)  that  there  was  no  planet  represented 
by  the  figures  28,  196,  and  388,  predicted  that  more  planets 
existed  and  should  be  looked  for.  It  does  not  appear  that 
VV.  Herschel  was  influenced  in  any  way  by  the  foregoing  figures 
as  regards  Uranus,  but  in  1800  some  German  observers,  six  in 
number,  assembled  at  Lilienthal  and  formed  themselves  into  a 
society  of  explorers,  under  Schroler  as  President,  to  search  for 
additional  planets.  Such  zeal  was  soon  rewarded,  and  the  first- 
fruits  were  the  planets  Ceres,  Pallas,  Juno,  and  Vesta.  No 
more  seeming  to  be  forthcoming,  the  work  was  abandoned  in 
1816  ;  but  a  Prussian  amateur  named  Hencke,at  Driesen,took  up 
the  work  on  his  own  account  about  1830,  but  with  no  immediate 
success. 


108  THE   LESS    KNOWN    PLANETS. 

The  discovery  of  Neptune  in  1846  infused  new  life  into  the 
movement  for  hunting  up  small  planets,  one  of  which  indeed, 
afterwards  named  Astraea,  had  been  found  on  December  8, 
1845,  by  Hencke  at  Driesen,  whose  single-handed  labour  has 
just  been  mentioned.  The  year  1846  produced  none.  Three 
were  found  in  1847,  one  in  1848,  one  in  1849,  three  in  1850,  and 
two  in  18.51.  Thenceforward  the  discoveries  became  much 
more  rapid,  and  by  the  end  of  1860  a  total  of  62  had  been 
reached  ;  1870  brought  the  number  up  to  in  ;  and  since  then 
they  have  grown  with  ever-increasing  rapidity  up  to  the  present 
total,  which  exceeds  700. 

The  system  of  looking  for  them  has  latterly  been  materially 
altered.  For  many  years  after  the  search  was  first  begun  it 
was  carried  out  very  much  on  the  lines  on  which  the  search  for 
Neptune  was  conducted,  namely,  by  ocular  comparison  of  the 
stars  visible  in  a  telescope  with  maps  of  the  stars  in  the  same 
locality  ;  but  of  recent  years  the  extensive  introduction  of  photo- 
graphy has  greatly  facilitated  the  discovery  of  new  planets.  I 
am  very  sceptical  as  to  the  usefulness  of  these  discoveries  being 
continued.  The  actual  interest  attaching  to  these  bodies  is  in 
nearly  every  case  nil,  and  the  labour  involved  in  keeping  pace 
with  their  record  and  in  calculating  their  orbits  is  out  of  all 
proportion  to  the  ultimate  useful  result.  That  this  would 
appear  to  be  the  opinion  of  astronomers  generally  is  shown  by 
the  fact  that  practically  the  whole  work  is  now  concentrated  in 
German  hands,  no  other  nation  seeming  to  pay  much  attention 
to  these  planets.  Under  these  circumstances,  I  shall  sum  up  in 
very  concise  form  the  rest  of  the  information  which  I  shall  give. 

It  will  excite  no  surprise  that  these  planets  are  in  a  constant 
state  of  confusion  as  regards  their  identity.  Let  us  suppose 
that  one  is  found  by  having  imprinted  itself  on  a  photographic 
plate  ;  the  question  at  once  arises,  Is  it  a  new  one  ?  or  is  it  an 
old  one  which,  having  been  missing,  has  turned  up  again  ?  Here 
are  endless  traps  for  the  astronomical  author  who  wishes  to 
make  an  accurate  enumeration  of  these  planets.  It  may  also 


THE    MINOR    PLANETS. 


109 


be  added  that  of  those  which  have  been  found  and  duly  enrolled 
no  fewer  than  sixty  are  now  ticked  off  as  "lost" — very  likely 
lost  for  ever  ;  or,  if  rediscovered,  may  never  have  their  positions 
at  rediscovery  brought  into  touch  with  their  positions  years 
ago,  and  so  proof  of  their  identity  may  never  be  attainable. 

These  objects  have  borne  various  generic  names.  "  Minor 
Planets  "  may  now  be  taken  as  their  recognised  name,  whilst 
the  name  first  proposed  for  them  by  Sir  W.  Herschel, 


Fig.  139. — How  Minor  Planets  are  recognised  as  such. 

"Asteroids,"  though  no  longer  recognised  by  the  scientific 
world,  is  nevertheless  a  designation  not  unfrequently  met  with. 
This  remark,  in  a  lesser  degree,  applies  also  to  the  name 
"  Planetoid."  As  regards  their  individual  names,  at  the  out- 
set names  taken  from  the  mythologies  of  ancient  Greece  and 
Rome,  together  with  the  old  Latin  names,  in  some  cases,  of  the 
places  of  discovery,  were  almost  exclusively  employed ;  but  of 
recent  years,  reasonable  names  having  become  exhausted, 


110  THE    LESS    KNOWN    PLANETS. 

invented   and   made-up  names,    many   of  them   of  the   most 
ridiculous  and  fantastic  character,  have  been  chosen. 

Female  Christian  names  abound,  the  origin  of  which  will 
often  not  bear  investigation  from  the  standpoint  of  dignity  and 
etiquette ;  for  instance,  the  planets  Lumen,  Bertha,  and  Zelia 
are  said  to  immortalise  the  daughters  of  a  well-known  French 
astronomer.  The  difficulty  now  of  finding  new  planets  and  of 
getting  hold  of  the  older  ones  is  sufficiently  shown  by  the 
successive  deterioration  which  has  taken  place  in  the  size  of 
those  discovered  as  discoveries  multiplied.  The  average 
brightness  of  the  first  ten,  reckoned  in  star  magnitude,  was  8J; 
of  the  second  ten  it  was  9^  ;  of  the  third  ten  it  was  io£  ;  of  the 
fourth  ten  it  was  n.  From  this  average  figure  the  average  has 
progressively  gone  down,  and  I  suppose  that  none  are  now 
found  which  are  brighter  than  the  I3th  or  I4th  magnitude — a 
sufficient  justification,  I  think,  for  saying  that  they  are  not 
worth  looking  after. 

The  4  oldest  and  Eros  are  really  only  those  in  the  slightest 
degree  worth  consideration.  Ceres  is  sometimes  as  bright  as 
a  star  of  the  7th  mag.,  and  sometimes  shines  with  a  reddish 
tinge,  and  has  been  thought  to  possess  an  atmosphere.  Pallas, 
when  nearest  the  Earth  at  Opposition,  is  of  the  7th  mag.,  and 
is  of  a  yellowish  tinge.  Juno  is  of  the  8th  mag.,  and  reddish. 
Vesta  is  the  brightest  of  the  lot,  and  occasionally  rises  to  the 
6th  mag.,  shining  with  a  light  which  some  consider  to  be  pure 
white,  while  others  ascribe  to  it  a  yellowish  tinge. 

After  these  4  oldest  and  probably  largest  of  the  Minor  Planets, 
the  only  one  which  has  any  intrinsic  interest  or  importance  is 
Eros.  The  annexed  diagram,  Fig.  140,  shows  the  fact  that 
Eros,  owing  to  the  character  of  its  orbit,  comes  on  occasions 
very  near  the  Earth,  and  on  that  account  is  available  for 
enabling  us  to  ascertain  the  distance  of  the  Earth  from  the 
Sun,  and  it  has  been  so  used  accordingly.  Unfortunately,  its 
existence  was  not  known  on  the  last  occasion,  in  which  it  was 
at  its  nearest  distance  to  the  Earth,  which  was  in  1894,  and  it 


THE    MINOR    PLANETS. 


Ill 


will  not  again  be  at  its   least  distance  from  the  Earth  until 
1924. 

As   regards   their   sizes,    Barnard  has   given   the   following 
figures  for  diameter  :  Ceres  520  miles,  Pallas  304,  and  Vesta 


MARS    333 


Fig.  140.— The  Orbits  of  Eros,  Mars,  and  the  Earth. 

211.  Except,  perhaps,  Juno,  Hornstein  thinks  that  none  of  the 
others  are  larger  than  25  miles  in  diameter,  and  most  of  them 
much  less — from  1 5  to  5  miles. 

One  remarkable  fact  about  these  planets  is  that  their  orbits 


112  THE    LESS    KNOWN    PLANETS. 

are  in  many  cases  much  more  inclined  to  the  Ecliptic  than  any 
of  the  orbits  of  the  older  planets.  Hence  the  term  "  ultra- 
zodiacal  planets"  was  once  suggested. 

Many  orbits  are  eccentric  to  a  very  extreme  degree  ;  No.  699 
seems  to  have  the  most  eccentric  orbit,  the  eccentricity 
amounting  to  0*412,  from  which  it  follows  that  its  perihelion 
distance  is  142,285,000  miles  and  its  aphelion  distance 
292,871,000  miles — remarkable  extremes. 

The  least  eccentric  orbit  is  that  of  No.  699  (unnamed),  in 
which  the  eccentricity  amounts  to  only  o'oio. 

The  most  inclined  orbit  is  that  of  Pallas  (2),  in  which  the 
inclination  amounts  to  34°  44'. 

The  least  inclined  orbit  is  that  of  Ortrud,  in  which  the 
inclination  amounts  to  only  o°  26'. 

Perhaps  it  will  appear  hereafter  that  there  is  one  other  planet 
with  an  inclination  less  than  this,  i893Y,  whose  inclination  is 
believed  to  be  only  o°  18'. 

The  planet  nearest  to  the  sun  is  Eros  (433),  which  revolves 
round  the  Sun  in  643  days,  or  1*76  years. 

The  honour  of  being  farthest  off  rests  with  Hector  (624), 
whose  period  is  12'!  years.  Hector  has,  as  its  nearest  neigh- 
bours, Achilles  (588),  Patroclus  (617),  and  Nestor  (659),  all 
three  with  periods  only  slightly  less  than  12  years. 

After  the  discovery  of  Pallas,  Olbers  suggested  that  Ceres 
and  Pallas  might  be  fragments  of  some  larger  planet  shattered 
by  some  great  catastrophe.  The  idea  sounds  plausible,  and 
certainly  is  attractive,  but  is  considered  to  be  impossible  on 
mathematical  grounds. 


CHAPTER   VIII. 
ECLIPSES. 

The  Principles  of  eclipses. — Other  kindred  phenomena. — Two  anec- 
dotes.— The  difference  between  eclipses  of  the  Sun  and  of  the  Moon. — 
Total  eclipses. — Partial  eclipses. — Annual  number  of  eclipses. — 
The  Saros. — Method  of  using  the  Saros. — Eclipses  of  the  Sun 
considered. — The  accompaniments  of  a  large  partial  eclipse  of  the 
Sun. — Of  a  total  eclipse. — The  terror  of  savages. — Instances  of 
this. — The  darkness. — The  fall  of  temperature. — The  red  flames. — 
Baily's  Beads. — The  Corona. — Details  relating  thereto.  —  The 
Moon's  shadow. — Shadow-bands. — Bushes  of  light. — The  Corona, 
a  solar  appendage. — Connection  between  its  shape  and  spots  on 
the  Sun. — Coming  eclipses. — Eclipse  expeditions. — Eclipses  of 
the  Moon. — The  Moon  when  totally  eclipsed. — Anecdote  of  Columbus. 
— Incident  in  the  South  African  War.— Transits  of  Mercury  and 
Venus. — Method  of  measuring  the  Sun's  distance. — Transits  and 
eclipses  of  the  satellites  of  Jupiter. — Occultation  of  planets  and 
stars  by  the  Moon. — Occultation  of  stars  and  planets  by  planets. 

THOUGH  the  title  of  this  chapter  is  given  as  "  eclipses  "  simply, 
the  reader  will  find,  when  he  gets  towards  the  end  of  it,  that 
it  includes  some  other  phenomena  which  are  of  kindred 
character,  and  which  are  technically  known  as  "  Transits  "  and 
"  Occupations." 

The  word  "  eclipse "  usually  brings  to  one's  mind  certain 
occasional  events  which  are  specially  connected  with  the  Sun 
and  the  Moon,  and  which,  so  far  as  their  principles  are  con- 
cerned, are  in  the  highest  degree  simple  ;  but,  simple  as  they 
are,  it  is  strange  how  little  they  are  understood  even  by  people 
of  education  and  position,  as  the  two  following  anecdotes  will 
show. 

8  "3 


114  ECLIPSES. 

Some    years    ago — less    than    twenty — there    lived    in    the 

town  of  two   sisters,  who  were  recognised  as  cultivated 

and  well-educated  women.  They  had  prepared  to  watch  an 
eclipse  of  the  Moon  which  began  on  one  day  but  ended  on 
another  day,  according  to  the  customary  civil  reckoning  ;  that 
is  to  say,  it  began  late  in  the  evening  of  one  day,  and  ended 
after  midnight  in  the  early  hours  of  the  next  day. 

Accordingly,  the  almanac  gave  the  date  as,  we  will  say, 
December  21-22.  Through  some  mischance  the  sisters  failed 
to  begin  to  watch  the  eclipse  on  the  evening  of  the  2ist,  and 
comforted  themselves  by  saying,  "  It  is  coming  again  to- 
morrow night,  because  the  almanac  says  that  it  will  happen  on 
the  2ist  and on  the  22nd  !  " 

The  second  anecdote  concerns  the   eclipse   of  the   Sun  of 

August  28,    1905.      A   royal   personage   then  at said  to 

a  gentleman  of  her  suite,  "  I  want  to  see  the  eclipse  to-day ; 
please  make  the  necessary  preparations  [smoked  glass,  etc.], 
and  call  me  at  the  proper  time  out  on  to  the  terrace."  Of 
course  she  received  a  suitable  answer,  which  included  the 
words,  "You  must  be  ready  at  ten  minutes  to  n."  The  hour 
of  10.50  arrived;  then  10.55  \  tnen  Ir  :  st^  no  royal  sight- 
seer on  the  terrace.  The  gentleman  sent  a  very  pressing 
message  into  the  house,  with  the  only  result  that  a  head 
appeared  out  of  an  upper  window,  followed  by  the  somewhat 
irritable  remark,  "  I'm  coming !  why  are  you  in  such  a 
hurry  ?  "  Which  not  unnaturally  evoked  the  reply,  "  I'm  not  in 
a  hurry,  ma'am  ;  but  the  eclipse  is  in  a  hurry,  and  you  are  likely 
to  lose  the  most  striking  feature  of  it." 

Eclipses,  commonly  so-called,  are  either  of  the  Sun  or  of  the 
Moon  ;  and  according  to  the  degree,  considerable  or  incon- 
siderable, of  the  loss  of  light  involved,  so  they  bear  different 
specific  names.  Eclipses  of  either  luminary  may  be  either 
"total"  or  "partial,'3  whilst  an  eclipse  of  the  Sun  may  also 
bear  a  third  name  :  it  may  be  "  annular." 

To  understand  the  general  principles  of  eclipses  should  not 


FIGS.  141  and  141  a 


PLATE  xxxvn 


AN     ERUPTIVE     PROMINENCE. 


A    QUIESCENT    PROMINENCE. 
"Red  Flames"  on  the  Sun,  now  generally  termed  "Prominences." 


ECLIPSES    OF    THE   SUN.  115 

be  a  difficult  matter,  bearing  in  mind  that  eclipses  of  the  Sun 
and  eclipses  of  the  Moon  depend  upon  totally  different 
principles. 

The  Moon,  in  the  course  of  its  monthly  journey  round  the 
Earth,  passes,  at  the  stage  of  New  Moon  always,  not  far 
from  the  Sun,  travelling  either  higher  in  the  heavens  or  lower 
in  the  heavens  than  the  actual  place  of  the  Sun.  But  on  rare 
occasions  it  may  happen  to  pass  quite  in  front  of  the  Sun. 
This  will  result  in  an  eclipse  of  the  Sun.  The  eclipse  will  be 
total  if  the  Moon  passes  centrally  over  the  Sun  and  the  Moon 
is  suitably  placed  in  its  orbit  to  cover  the  whole  of  the  Sun  ;  it 
will  be  annular  if  the  Moon,  though  centrally  placed  in  front 
of  the  Sun,  is  not  large  enough  to  cover  the  whole  of  the  Sun  ; 
it  will  be  partial  if  it  passes  only  over  the  upper  portion 
of  the  Sun  or  the  lower  portion.  Something  also  depends 
upon  the  position  on  the  Earth  of  the  observer.  One  observer, 
A.  B.,  may  be  so  placed  that  the  centre  of  the  Earth,  the  centre 
of  the  Moon,  and  the  centre  of  the  Sun  are  all  exactly  in  the 
same  straight  line.  A.  B.  will  therefore  see  a  central  and  total 
eclipse. l 

Another  observer,  A.  B.'s  brother,  whom  we  will  call  B.  B.,  is 
on  the  Earth  in  a  latitude  several  hundred  miles  more  northerly 
or  more  southerly  than  A.  B.  To  such  a  one  the  Moon  will 
be  displaced  from  the  position  in  which  A.  B.  sees  it  :  B.  B.  will 
therefore  only  see  the  Moon  passing  over  the  southern  or  the 
northern  part  of  the  Sun.  He  will  therefore  only  see  a  partial 
eclipse. 

If  the  Moon  were  always  at  the  same  distance  from  the 
Earth,  and  Earth  and  Moon  were  always  at  the  same  distance 
from  the  Sun,  every  eclipse  might  be  total,  and  would  be  the 
same  ;  that  is  to  say,  the  Sun  would  always  be  covered  with 
the  same  overlap,  and  the  time  during  which  it  remained 
covered  would  be  always  the  same. 

But  the  distances  referred  to  are  not  always  the  same  ;  they 

1  Unless  it  is  only  an  annular  one, 


jl6  ECLIPSES. 

vary  considerably.  It  follows  therefore  that  if,  when  the  Moon 
is  nearest  the  Earth,  the  Sun  should  be  at  its  farthest  possible 
distance  from  the  Earth,  the  Moon  would  look  its  largest  and 
the  Sun  would  look  its  smallest.  This  would  have  the  effect  of 
making  the  overlap  during  totality  the  largest  possible,  and 
therefore  the  duration  of  the  Sun's  invisibility  the  longest 
possible.  If,  on  the  other  hand,  the  Moon  was  at  its  greatest 
distance  from  the  Earth,  and  the  Sun  at  its  nearest,  the  Moon 
would  look  its  smallest  and  the  Sun  its  largest.  Under  such 
circumstances,  the  Moon  would  be  too  small  to  conceal  the 
whole  of  the  Sun  ;  and  such  are  the  circumstances  under  which 
the  eclipse  would  be  annular  to  an  observer  viewing  it  from 
such  a  latitude  on  the  Earth  as  would  make  the  Earth,  the 
Moon,  and  the  Sun  to  be  in  the  same  straight  line. 

Another  consequence  follows  from  the  ever-varying  position  of 
the  Moon  as  regards  its  distance  from  the  Earth.  An  eclipse 
may  be  total  at  one  place,  but  in  the  course  of  an  hour  or  two 
the  Moon's  distance  from  the  Earth  may  have  varied  so  that  it 
has  become  more  distant  and  therefore  looks  smaller,  and  an 
observer  on  the  Earth  and  on  the  central  line  at  the  same  time 
will  see  that  the  apparent  diameter  of  the  Moon  has  become 
diminished,  so  that  it  is  no  longer  large  enough  to  cover  »the 
whole  of  the  Sun.  To  such  an  observer  the  eclipse  will  rank 
as  an  annular  or  semi-annular  one.  Such  was  the  eclipse  of 
April  17,  1912. 

Turn  we  now  to  eclipses  of  the  Moon.  Though,  so  far  as 
names  go,  such  eclipses  are  either  "  total "  or  "  partial,"  yet 
the  totality  or  partiality  depends  upon  principles  quite  different 
from  those  which  bring  about  the  same  nominal  results  in  the 
case  of  the  Sun. 

The  Earth  and  the  Moon  being  both  illuminated  by  the  Sun, 
both,  of  course,  cast  a  shadow  into  space,  just  as  every  opaque 
object  put  in  front  of  a  source  of  light  has  its  shadow  thrown 
behind  it.  If,  therefore,  at  the  time  that  the  Moon  is  in  that 
position  of  its  orbit  known  as  the  Opposition  (when  it  is  on  the 


FIG.   142 


PLATE    XXXVIII. 


116] 


Solar  Eclipses  visible  in  England,  1891-1922. 


FIG.   143 


PLATE    XXXTX. 


ECLIPSES    OF   THE    MOON.  117 

meridian  at  midnight),  and  Moon,  Earth,  and  Sun  happen  to 
be  exactly  (or  nearly)  in  the  same  straight  line,  the  Moon,  in 
its  progress  round  the  Earth,  will  plunge  into  the  Earth's 
shadow,  either  wholly  or  partly,  and  the  result  will  be  that 
the  Moon  will  be  wholly  or  partly  lost  to  the  view  of  all  the 
inhabitants  of  the  hemisphere  which  is  turned  away  from  the 
Sun.  The  Moon,  when  completely  plunged  in  the  Earth's 
shadow,  may  either  become  completely  invisible  or  signs  of  its 
presence  in  the  sky  may  be  obtainable  from  the  fact  that  a  faint 
reddish  tinge  seems  to  pervade  its  surface,  and  so  keeps  it 
dimly  in  view.  This  visibility  or  invisibility  has  nothing  to  do 
with  the  principles  of  the  eclipse  ;  but  I  shall  discuss  the 
matter  under  another  head  later  on. 

It  is  now  time  to  go  somewhat  more  fully  into  details  re- 
specting these  eclipses.  If  the  orbits  of  the  Earth  and  the 
Moon  were  in  the  same  plane  an  eclipse  of  the  Sun  would 
happen  once  in  every  month  at  the  epoch  of  New  Moon  ;  and 
an  eclipse  of  the  Moon  would  also  happen  every  month  at  the 
epoch  of  Full  Moon  ;  but  the  Moon  moves  round  the  Earth 
in  an  orbit  which  is  inclined  to  the  ecliptic  at  an  angle  of 
about  5°,  and  therefore  it  is  only  on  occasions  that  the  Moon 
will  be  found  immediately  in  front  of  the  Sun  so  as  to  bring 
about  an  eclipse  of  the  Sun,  or  immediately  behind  the  Earth 
(looked  at  from  the  Sun),  and  so  bring  about  an  eclipse  of  the 
Moon.  The  effect  of  this  inclination,  coupled  with  certain  other 
disturbed  conditions  which  subsist  with  respect  to  the  Moon's 
orbit,  brings  about  a  result  that  the  possible  number  of  eclipses 
in  the  course  of  a  year  are  limited,  and  vary.  There  must 
always  be  two,  and  cannot  be  more  than  seven,  eclipses  in  a 
year.  When  there  are  only  two  they  must  always  be  of  the 
Sun.  In  the  case  of  the  seven,  five  of  them  may  be  solar,  in 
which  case  only  two  can  be  lunar,  though  under  no  circum- 
stances can  there  be  more  than  three  lunar  eclipses  in  one 
year,  and  in  some  years  there  may  be  none  at  all. 

If  the  almanacs  for  a  few  successive  years  are  consulted  it 


Il8  ECLIPSES. 

would  seem  that  the  succession  of  the  eclipses  is  Very  irre- 
gular, yet  that  is  not  so  in  reality  if  the  almanacs  of  18 
successive  years  are  consulted,  and,  better  still,  the  almanacs 
of  thrice  that  period,  or  54  years,  are  examined.  If  either 
or  both  of  these  things  are  done  it  will  be  found  that  eclipses 
recur  almost  in  the  same  order  every  18  years  10  days,  or  in 
every  54  years  31  days. 

This  fact  was  known  more  than  3000  years  ago  to  the 
Chaldaean  astronomers.  They  called  the  scheme  the  "  Saros," 
and  it  furnished  them,  as  it  would  furnish  us,  with  the  means 
of  predicting  eclipses  for  any  number  of  years  in  advance. 
It  does  something  more,  for  it  not  only  enables  the  amateur 
to  predict  eclipses  for  himself,  but  also  enables  him  to  say  in 
advance  what  will  approximately  be  the  path  of  an  eclipse 
across  the  Earth.  If  we  take  any  given  eclipse,  say  of  the 
Sun,  visible  at  any  particular  place,  a  nearly  similar  eclipse 
will  be  visible  nearly  in  the  same  locality  18  years  and 
10  days  later,  but  the  locality  will  be  a  certain  number  of 
miles  different,  and  S.  of  the  previous  line  of  central  eclipse. 

To  give  a  concrete  instance.  There  was  a  total  eclipse  of 
the  Sun  visible  in  the  north  of  Norway  on  August  9,  1896,  at 
the  hour  of  4.30  in  the  morning.  That  eclipse  will  recur 
on  August  21,  1914,  but  the  central  line,  still  in  Norway,  will 
be  so  many  miles  S.  of  the  line  of  1896,  and  the  time  will 
be  much  more  convenient,  because  it  will  be  nearer  the  break- 
fast-hour of  most  people.  The  gradual  transformation  of  the 
central  lines  of  eclipses  will  be  realised  by  a  perusal  of  the 
following  particulars  of  the  eclipse  of  the  Sun  of  June  1295, 
when  it  appeared  at  the  North  Pole.  In  1367  it  had  got 
forwards  to  the  month  of  August,  and  southwards  to  the  North 
of  Europe  ;  in  1439  it  was  visible  all  over  Europe  ;  at  its  nine- 
teenth appearance  in  1601  it  was  central  in  London  ;  on  May  5, 
i Si 8,  it  was  also  visible  in  London,  and  was  again  nearly 
central  in  the  metropolis  on  May  15,  1836.  At  its  next  ap- 
pearance on  May  26,  1854,  the  central  line  passed  over  North 


ECLIPSES    OF    THE   SUN.  1 19 

Africa  ;  on  June  6,  1872,  it  crossed  France  ;  on  June  17,  1890, 
it  crossed  North  Africa  and  Turkey  in  Asia ;  on  June  28,  1908, 
it  was  central  in  Mexico,  Florida,  and  across  the  Atlantic  to 
Senegambia.  At  its  thirty-ninth  appearance  on  August  10, 
1980,  the  Moon's  shadow  will  pass  S.  of  the  Equator,  and, 
as  the  eclipse  will  take  place  near  midnight,  it  will  be  invisible 
in  Europe,  Africa,  and  Asia,  and  visible  only  in  South  America. 
At  every  subsequent  period  the  eclipse  will  go  more  and  more 
towards  the  S.,  until  at  its  seventy-eighth  appearance  on 
September  30,  2665,  it  will  go  off  at  the  South  Pole  of  the 
Earth,  and  therefore  the  series  will  have  ended. 

Thus  far  we  have  been  considering  eclipses  of  the  Sun  and 
Moon  as  mixed  up  in  regard  to  certain  general  principles  ;  but 
we  must  now  deal  with  solar  and  lunar  eclipses  separately, 
because  they  differ  so  much  in  the  details  relating  to  their 
observation  that  it  is  necessary  to  keep  them  distinct.  An 
eclipse  of  the  Sun  in  cases  where  only  a  portion  of  the  Sun 
is  obscured  offers  really  no  features  of  interest  unless  the 
portion  obscured  is  very  large,  not  less  than  nine-tenths  of  the 
Sun's  diameter.  When  this  amount  of  obscuration  occurs  there 
are  a  few  subsidiary  occurrences  calculated  to  interest  the 
student  of  nature  ;  for  instance,  the  reduction  in  the  sunlight 
available  for  lighting  up  the  landscape  is  very  marked,  and, 
though  not  a  cloud  is  visible,  yet  the  sky  puts  on  a  dark,  lurid 
appearance  suggestive  of  a  severe  thunderstorm  being  at  hand. 
The  temperature  of  the  air  becomes  much  reduced,  perhaps  to 
the  amount  of  5°  Fahrenheit,  or  even  more,  and  the  personal 
sensation  of  chilliness  experienced  is  even  greater  than  the 
thermometer  implies.  Birds  distinctly  manifest  their  know- 
ledge that  something  special  is  taking  place,  for,  even  if  they 
do  not  definitely  go  to  roost,  they  are  evidently  uncomfortable 
and  suspicious.  If  any  trees  near  are  in  leaf  images  of  the 
crescent  Sun  will  be  cast  on  flat  surfaces  such  as  a  boarder 
even  a  book,  laid  on  the  ground  so  that  images  of  the  Sun 
may  pass  through  the  foliage.  Finally,  the  maximum  phase  is 


t20  ECLIPSES. 

accompanied  by  a  sudden  gust  of  wind.  All  these  phenomena 
were  seen  in  different  parts  of  England  on  the  occasion  of  the 
large  eclipse  of  April  17,  1912. 

It  is  when  a  total  eclipse  of  the  Sun  happens  that  a  solar 
eclipse  shows  to  the  greatest  advantage,  many  of  the  features 
manifested  being  of  a  very  sensational  character,  the  excite- 
ment of  the  spectators  being  greatly  accentuated  by  the 
rapidity  with  which  the  transformations  take  place,  and  the 
limited  amount  of  time  available  for  looking  at  them.  I  am 
here  speaking  of  eclipses  of  the  Sun  observed  by  educated 
and  sensible  people,  who  know  all,  or  at  any  rate  something, 
about  the  matter.  But  when  the  spectators  comprise  ignorant 
natives,  whether  Indians  or  Negroes  or  Aborigines  generally, 
a  total  eclipse  of  the  Sun  is  usually  the  occasion  of  remarkable 
scenes  in  which  alarm  and  despair  and  anger  are  intermingled. 
From  the  various  records  which  I  have  gathered  up  of  such 
scenes,  I  select  the  following  as  typical  of  many  such  narra- 
tives. But  the  first  quotation  will  show  that  we  need  not  go  so 
far  off  as  the  lands  inhabited  by  Indians  for  an  example  of  an 
eclipse  panic. 

The  Earl  of  March  quotes  from  a  letter  written  by  a  certain 
Sir  Thomas  Prendergast,  from  Pantglase,  under  date  of 
August  3,  1748,  the  following  sentence  : 

"  I  would  have  spun  out  a  few  lines  more  in  relation  to  the 
eclipse,  such  as  the  care  taken  to  get  in  all  the  hay  before  it ; 
prayers  said  in  churches,  preparatory  and  preventive  ;  and 
many  other  demonstrations  of  terror  and  religion."  l 

What  happened  on  the  occasion  of  the  total  eclipse  of 
July  29,  1878,  was  thus  described  in  an  American  newspaper 
by  a  spectator  resident  at  Fort  Sill,  Indian  Territory  : 

"  On  Monday  last  we  were  permitted  to  see  the  eclipse  of  the 
Sun  in  a  beautiful  bright  sky.  Not  a  cloud  was  visible.  We 
had  made  ample  preparation,  laying  in  a  stock  of  smoked  glass 

1  "A  Duke  and  his  Friends"  (London,  1911). 


FIG.   144 


PLATE    XL. 


The  Solar  Corona,  July  29,  1878  (/.  P.  Murphy}. 


I20l 


FIGS.  145-146 


PLATE    XL1. 


The  Solar  Corona,  August  29,  1886  (Harvard  Annals,  xviii.), 


The  Solar  Corona,  Dec.  22,  1889  (Perry}. 


TOTAL    ECLIPSES    OF    THE    SUN.  121 

several  days  in  advance.  It  was  the  grandest  sight  I  ever 
beheld;  but  it  frightened  the  Indians  badly.  Some  of  them 
threw  themselves  upon  their  knees  and  invoked  the  Divine 
blessing  ;  others  flung  themselves  flat  on  the  ground,  face 
downward  ;  others  cried  and  yelled  in  frantic  excitement  and 
terror.  Finally,  one  old  fellow  stepped  from  the  door  of  his 
lodge,  pistol  in  hand,  and,  fixing  his  eyes  on  the  darkened  Sun, 
mumbled  a  few  unintelligible  words,  and,  raising  his  arm,  took 
direct  aim  at  the  luminary,  fired  off  his  pistol,  and,  after  throwing 
his  arms  about  his  head  in  a  series  of  extraordinary  gesticula- 
tions, retreated  to  his  own  quarters.  As  it  happened,  that  very 
instant  was  the  conclusion  of  totality.  The  Indians  beheld 
the  glorious  orb  of  day  once  more  peep  forth,  and  it  was 
unanimously  voted  that  the  timely  discharge  of  that  pistol 
was  the  only  thing  that  drove  away  the  shadow  and  saved 
them  from  the  public  inconvenience  that  would  have  certainly 
resulted  from  the  entire  extinction  of  the  Sun." 


We  will  now  go  back  to  the  general  concomitants  of  a 
total  eclipse  of  the  Sun  as  they  present  themselves  to  a  rational 
observer,  who  can  deal  with  the  matter  in  a  calm  and  philoso- 
phical spirit.  When  the  Moon  has  reached  the  Sun,  and  its 
forward  limb  has  broken  in  upon  the  Sun's  disc,  nothing 
remarkable  is  to  be  noted  until  the  Moon's  movement  has  so 
far  progressed  as  to  have  made  a  substantial  encroachment  on 
the  Sun.  When  perhaps  half  of  the  Sun  has  become  obscured 
a  fall  in  the  temperature  of  the  air  around  the  observer  will 
begin  to  be  felt.  The  next  thing  which  will  be  noticed  will  be 
a  change  in  the  appearance  and  colour  of  the  sky.  The 
ordinary  blue  will  become  much  deeper,  soon  passing  into  a 
dull  dark  slate  colour  which  will  eventually  reach  purple. 

This  purple  colour  has  been  likened  to  a  canopy  overhanging 
the  sky  nearly,  but  not  quite,  down  to  the  horizon  ;  for  the 
lowermost  strip,  so  to  speak,  of  the  canopy  reaching  actually  to 
the  horizon  is  not  purple,  but  orange,  more  or  less,  in  colour, 
which  hue  is  due  to  the  fact  that  the  Sun's  light  which  reaches 
the  observer  from  the  horizon  has  to  pass  through  a  very  thick 


*22  ECLIPSES. 

stratum  of  atmosphere  which  absorbs  much  of  the  violet  light  of 
the  spectrum. 

This  will  indicate  that  the  total  phase  is  at  hand,  and  that 
instant  and  the  two  or  three  minutes  (according  to  circum- 
stances) which  will  follow  constitute  the  high-water  mark  of  the 
excitement  of  the  spectators.  Though  the  duration  of  totality 
might,  according  to  theory,  reach  such  an  extreme  as  seven 
minutes,  this  extreme  never  is  reached,  and  from  two  to  four 
minutes  is  the  general  duration  of  the  eclipses  which  have  been 
observed  during  recent  years.  This  means  that  an  immense 
amount  of  work,  such  as  photographing  and  note-taking,  has  to 
be  compressed  into  a  very  limited  amount  of  time,  and  amid 
much  nervous  excitement. 

The  first  feature  which  suddenly  springs  into  view  are  jets  of 
Red  Flames,  now  more  generally  called  Prominences,  which 
spring  up  at  various  points  round  the  Sun's  circumference.  It 
was  at  one  time  supposed  that  these  Red  Flames  were  only  to 
be  seen  during  total  eclipses,  but  modern  instruments  and 
methods  have  brought  it  about  that  they  can  always  be  seen, 
so  far  as  their  positions  and  shapes  are  concerned.  These 
Red  Flames  are  now  recognised  to  be  masses  of  incandescent 
gas  mixed  with  other  gases,  one  of  which,  now  called  helium, 
is  not  found  on  the  Earth. 

Almost  coincident  with  the  appearance  of  the  Red  Flames,  or 
even  before  them,  numerous  beads  of  light  spring  up  along  the 
forward  limb  of  the  Moon.  These  are  known  as  "  Baily's 
Beads,"  having  been  first  systematically  described  by  the  late 
Mr.  Francis  Baily  in  1836.  Their  explanation  is  somewhat 
obscure.  It  has  been  supposed  that  they  are  outstanding 
portions  of  the  solar  disc  peeping  through  lunar  valleys,  whilst 
the  adjacent  mountains  project  far  beyond  the  smooth  circular 
outline  of  the  Sun's  disc,  which  is  no  longer  visible  as  a  con- 
tinuous circle.  This  may  be  one  of  the  causes  which  give  rise 
to  the  Baily's  Beads,  but  the  optical  phenomenon  known  as  the 
irradiation  of  light  is  no  doubt  a  contributory  cause. 


TOTAL    ECLIPSES    OF    THE   SUN.  123 

The  most  important  feature  of  a  total  eclipse  of  the  Sun  is 
the  Corona,  but  there  is  so  much  to  be  said  about  this  that  it 
will  be  preferable  to  dispose  of  the  other  accessory  details  of  a 
total  eclipse  before  embarking  on  the  Corona. 

The  first  and  most  obvious  proof  that  the  moment  of  totality 
has  been  reached  is  the  general  darkness  (virtually  that  of 
night)  which  prevails  everywhere,  darkness  usually  so  great  as 
to  necessitate  the  use  of  lamps  for  reading  clocks  and  watches. 
This  intense  degree  of  darkness  is  not,  however,  invariably 
experienced,  for  under  special  circumstances  which  cannot 
always  be  foreseen  or  explained  the  darkness  is  very  much  less 
intense  than  the  typical  darkness  just  alluded  to.  The  two 
total  eclipses  which  I  have  had  the  good  fortune  to  witness 
were  marked  by  both  these  characteristics.  During  the  eclipse 
of  1900  the  darkness  was,  I  apprehend,  normal,  but  in  1905  the 
darkness  may  be  described  as  having  been  rather  disappointing. 
The  evident  cause  was  the  prevalence  of  so  much  cloud  all  over 
the  sky,  and  probably  that  would  be  the  explanation  of  all  cases 
in  which  the  darkness  was  not  very  intense.  But  incidentally 
the  special  circumstances  of  any  particular  eclipse  would  have 
to  be  taken  into  account.  The  duration  and  the  extent  of  the 
apparent  overlapping  of  the  Sun  by  the  Moon,  whether  much 
or  little,  would  certainly  affect  the  intensity  of  the  resulting 
obscurity. 

The  shadow  cast  by  the  Moon  on  the  Earth  of  course  moves 
progressively  along  the  recognised  central  line  of  the  eclipse, 
and  its  movement  can  be  seen  and  followed  by  an  observer 
suitably  placed.  The  words  "  suitably  placed,"  in  this  connection, 
mean  that  the  spectator  occupies  an  elevated  position,  say  on 
the  top,  or  high  up  on  the  side,  of  a  hill,  or  on  the  top  of  a 
church-tower— that  is  to  say,  occupies  some  coign  of  vantage 
which  enables  him  to  scan  a  far-distant  horizon.  Doing  this,  he 
will  be  able  to  catch  sight  of  the  shadow  coming  up  to  his  own 
position,  hanging  over  it  momentarily,  and  then  rapidly  pass- 
ing off  in  the  opposite  direction.  The  necessity  for  an  observer 


124  ECLIPSES. 

being  wide  awake  who  is  desirous  of  catching  sight  of  this 
shadow  will  be  understood  by  the  statement  that  it  travels  at 
the  rate  of  thirty  miles  in  a  minute. 

Another  very  curious  and  interesting  feature  of  a  total 
eclipse  of  the  Sun  is  one  which  has  only  come  into  prominence 
of  recent  years,  namely  the  "  Shadow  Bands."  They  become 
visible  a  few  minutes  before  totality,  say  five.  They  are  wavy 
streaks  of  light  and  shade  which  dance  across  the  landscape, 
and  are  best  seen  if  the  observer  can  so  place  himself  as  to  face 
an  upright,  white-plastered,  or  stone  wall  to  serve  as  a  screen  to 
receive  the  shadows  as  they  pass  along.  Nothing  is  known  of 
their  cause,  or  of  any  laws  which  regulate  them.  They  vary  at 
different  eclipses  in  distance  apart,  in  breadth,  and  in  the  speed 
with  which  they  travel. 

One  other  thing  may  be  mentioned  :  the  brushes  of  light  which 
precede  the  immediate  appearance  of  the  Corona  on  the  side  of 
the  dark  Moon  opposite  to  the  disappearing  crescent  of  the  Sun. 
It  does  not  seem  that  these  brushes  of  light  are  directly  associa- 
ted either  with  the  Corona  or  with  Baily's  Beads,  or  indeed  with 
any  phenomenon  already  mentioned.  They  appear,  in  point  of 
fact,  to  have  an  entirely  independent  existence,  and  I  am  not 
acquainted  with  any  well-considered  explanation  of  their  origin. 

The  Corona  is,  after  all,  the  one  special  feature  of  every  total 
eclipse  of  the  Sun  on  which  every  observer,  as  a  rule,  concen- 
trates his  attention,  lunless  he  is  officially  turned  off  to  some- 
thing else.  Briefly  described,  the  Corona  is  a  broad  ring  of  light 
seen  to  surround  the  Moon  at  the  instant  of  totality,  lasting 
during  totality,  and  disappearing  on  the  return  of  the  Sun  to 
visibility.  It  is  usual  to  consider  the  Corona  in  a  twofold 
aspect— that  is  to  say,  we  speak  of  the  "  inner  Corona  "  and  the 
"  outer  Corona."  The  two  together  constitute  a  broad  bright 
ring  of  light  of  varying  diameter,  or  perhaps  it  will  be  best  to 
consider  the  inner  Corona  as  a  ring  averaging  £°  in  breadth, 
whilst  the  outer  Corona  extends  i,  2,  or  more  degrees  from  the 
Sun,  at  which  distance  it  generally  has  ost  its  more  or  less 


FIG.   147 


PLATE    XL! I. 


124] 


The  Solar  Corona,  1898  (C.  Michie  Smith], 


FIG.   148 


PLATE    XLII1. 


[125 


THE    CORONA.  125 

circular  outline,  its  edges  developing  into  long  rays  or  streamers 
of  varying  length,  and  stretching  from  various  parts  of  the  Sun's 
circumference.  I  say  "  Sun's  circumference  "  because  it  is  now 
well  understood  that  the  Corona  belongs  to,  and  is  an  appendage 
of  the  Sun,  but  looked  at  merely  from  the  sight-seeing  point  of 
view  it  might  equally  seem  to  be  a  ring  around  and  belonging 
to  the  Moon.  Indeed,  in  early  days  it  was  considered  to  be  a 
lunar  appendage,  and  it  was  only  during  recent  years  that  it  has 
become  certainly  established  that  the  Corona,  whatever  it  is, 
belongs  exclusively  to  the  Sun.  Its  general  appearance  will  be 
best  understood  by  a  careful  examination  of  the  accompanying 
illustrations,  which  represent  its  appearance  at  many  different 
dates,  and  as  portrayed  by  various  observers  ;  some  by  resort  to 
hand-drawing,  but  the  majority  due  to  photography. 

By  far  the  most  interesting  recent  discovery  connected  with 
the  Corona  is  the  fact  that  its  variations  in  shape  depend  upon 
an  undoubted  law,  but  the  circumstances  of  that  law  are  not  all 
understood.  The  law,  stated  baldly,  is  that  the  outline  of  the 
Corona  varies  in  a  most  marked  degree  according  to  whether 
the  eclipse  coincides  (or  nearly  coincides)  in  point  of  time  with  an 
epoch  of  maximum  or  an  epoch  of  minimum  Sun-spots.  In  the 
former  case  the  general  outline  of  the  Corona  is  roughly  circular 
and  compact,  whilst  in  the  latter  case  it  is  not  only  exceedingly 
irregular,  but  is  characterised  by  remarkable  streamers  extend- 
ing 2°  or  more  on  each  side  of  the  Sun  in  prolongation  of  the 
solar  Equator,  accompanied  by  narrow  flames  of  light  at  either 
pole. 

Speaking  generally,  I  think  we  are  entitled  to  assume  that 
the  Corona  is  something  in  the  nature  of  an  atmosphere  sur- 
rounding the  Sun  ;  but  its  indescribable  texture  (so  to  speak), 
and  the  uncertainty  and  irregularity  of  its  streamers,  and  its 
undoubted  connection,  in  some  way,  with  the  presence  or 
absence  of  Spots  on  the  Sun  render  it  one  of  the  great  mysteries 
of  modern  astronomy,  the  perfect  unravelling  of  which  has  yet 
to  be  accomplished. 


126  ECLIPSES. 

A  question  is  often  put  by  that  well-known  personage,  "  the 
man  in  the  street,"  in  the  dual  form  of  "  What  is  the  good  of  an 
eclipse  of  the  Sun  ?"  and  "  What  is  the  good  of  taking  so  much 
trouble  and  incurring  so  much  expense  to  observe  an  eclipse  of 
the  Sun  ?"  Perhaps  no  very  direct  answer  can  be  given,  and  a 
cynical  mind  might  take  pleasure  in  recalling  Sir  George 
Cornwall  Lewis's  classic  denunciation  of  astronomy,  which  he 
stigmatised  as  a  "  science  of  pure  curiosity."  The  remark, 
though  by  no  means  fair  or  strictly  accurate  if  applied  to  the 
science  of  astronomy  as  a  whole,  has  some  application  to  the 
special  subject  of  Eclipses.  They  are  only  observed  and  can 
only  be  observed  to  satisfy  human  curiosity,  which  desires  to 
know  as  much  as  possible  about  the  occult  things  of  the  universe, 
in  this  case  the  physical  constitution  of  the  Sun,  well  described 
by  Proctor  in  the  title  of  one  of  his  books  as  the  "  Ruler,  Light, 
Fire,  and  Life  "  of  the  system. 

The  elaborate  observations  of  the  last  35  years  in  par- 
ticular have  thrown  a  flood  of  light  on  the  origin  of 
those  phenomena  which  form  the  accessories  of  a  total 
eclipse  of  the  Sun,  and  so  indirectly  help  to  reveal  the  con- 
stitution of  the  Sun.  Of  the  special  sights  which  present 
themselves  during  a  total  eclipse,  beyond  doubt  the  Corona  is 
the  most  interesting  and  most  striking.  In  the  early  days  of 
exact  observations  the  question  was  long  in  controversy  whether 
the  Corona  was  connected  with  the  Moon  or  the  Sun.  It  is 
now  a  matter  of  perfect  certainty,  as  has  been  already  stated, 
that  the  Corona  is  a  solar  and  not  a  lunar  feature,  and  that  the 
Moon  has  only  a  secondary  share  in  the  matter  for  the  reason 
that  its  own  solid  body  blocks  out  the  sunlight  from  observers 
on  the  Earth,  and  so  enables  them  to  see  the  display  of  light 
which  emanates  from  the  Sun  and  constitutes  the  Corona. 

The  question  of  the  shape  of  the  Corona,  as  connected  with 
the  prevalence  of  Sun-spots,  is  such  an  important  one  that  it 
is  worth  while  to  recapitulate  the  facts  in  a  slightly  different 
form;  thus  :  When  a  total  eclipse  of  the  Sun  occurs  at  or 


FORTHCOMING    ECLIPSES.  127 

near  the  epoch  of  the  Sun-spot  maximum,  the  Corona  takes 
a  distinctly  compact  shape,  with  its  outline  of  very  much  the 
same  breadth  all  the  way  round  the  Sun,  whatever  streamers  or 
special  off-shoots  may  be  visible.  On  the  other  hand,  when 
an  eclipse  occurs  at  an  epoch  of  Sun-spot  minimum,  there  is 
a  marked  deficiency  in  the  breadth  of  the  Corona  at  the 
N.  and  S.  poles  of  the  Sun,  but  in  the  equatorial  regions, 
both  E.  and  W.,  the  Corona  throws  out  broad,  elongated 
streamers,  which  on  some  occasions  have  been  traced  to  a 
distance  of  4°  from  the  Sun's  limbs.  The  meaning  of  these 
differences  is  at  present  unknown,  but  the  facts  are  unquestion- 
able. It  is  interesting  to  note  that  the  eclipse  of  1900  was 
the  first  that  was  made  the  subject  of  a  prediction,  that  as  it 
coincided  with  an  epoch  of  few  or  no  Sun-spots,  its  outline 
would  be  elongated  in  the  Sun's  equatorial  regions  ;  and  this 
proved  to  be  the  case. 

The  Corona  itself  is  no  new,  or  even  modern,  discovery. 
The  record  of  its  existence  certainly  goes  back  to  1567,  and 
perhaps  even  much  further  than  that.  What  is  modern  and 
newly  recognised  is  that  the  general  outline  of  the  Corona 
varies  periodically,  with  some  relation  to  the  spots  on  the  Sun. 

It  may  interest  the  reader  to  hear  something  about  the 
eclipses  which  will  happen  during  the  next  few  years.  The 
information  which  follows  is  taken  chiefly  from  the  Nautical 
Almanac,  and  the  Rev.  S.  J.  Johnson's  Historical  and  Future 
Eclipses. 

1913,  March  22. — Total  eclipse  of  the  Moon,  invisible  at 
Greenwich,  but  visible  in  Polynesia.  (Mag.  \'$j6.} 

1913,  April  6. — Partial  eclipse  of  the  Sun,  invisible  at  Green- 
wich, visible  in  North- West  America  and  North-East  Asia. 

1913,  September  i. — Partial  eclipse  of  the  Sun,  invisible  at 
Greenwich,  visible  in  Labrador.  (Mag.  O'i5.) 

1913,  September  15. — Total  eclipse  of  the  Moon,  invisible  in 
Greenwich,  visible  in  the  Indian  Ocean.  (Mag.  1*43.) 

1913,  September  it). — Partial  eclipse  of  the  Sun,  invisible  at 
Greenwich,  visible  in  the  South  Polar  regions.  (Mag.  0*82.) 


128  ECLIPSES. 

1914,  February  24.—  Annular  eclipse  of  the  Sun,  visible  only 
in  the  South  Polar  Regions. 

1914,  March  12. — Partial  eclipse  of  the  Moon,  partly  visible 
at  Greenwich  in  the  early  morning. 

1914,  August  21. — Total  eclipse  of  the  Sun,  visible  at  Green- 
wich as  a  partial  eclipse  (Mag.  0^65 1).  The  central  line  passes 
through  Southern  Russia,  north-westwards  through  Norway. 

1914,  September  4. — Partial  eclipse  of  the  Moon,  invisible  at 
Greenwich,  and  visible  only  in  Polynesia. 

The  foregoing  statement  of  the  eclipses  of  1913  and  1914 
embraces  all  the  eclipses  of  these  years,  but  considerations  of 
space  require  me  now  to  continue  the  statement  on  a  principle 
of  selection,  and  I  give,  therefore,  now  only  eclipses  of  the  Sun, 
and  only  such  as  are  either  annular  or  total,  and  also  visible 
either  in  England  or  within  easy  reach  of  England. 

1916,  February  3. — Total  eclipse  visible  in  the  Atlantic,  just 
missing  the  shores  of  Ireland. 

1921,  April  8. — Annular  eclipse,  visible  about  the  Shetland 
Islands. 

I925?  January  24. — Total  eclipse,  visible  in  North  America 
and  across  the  Atlantic  to  beyond  the  N.  of  Scotland. 

1927,  June  29. — Total  eclipse,  visible  in  North  Wales,  Lan- 
cashire, North  Yorkshire,  and  Durham,  but  total  for  only  about 
20  seconds  or  a  little  more.  This  eclipse  is  actually  the  first 
total  eclipse  visible  at  all  in  England  since  1724. 

After  1927,  England  will  have  no  chance  of  another  total 
eclipse  until  August  n,  1999,  when  the  shadow-line  will  cross  a 
part  of  Cornwall  and  Devonshire.1  In  point  of  fact,  many 
centuries  will  elapse  ere  another  eclipse  will  occur  fulfilling  the 
four  following  conditions  presented  by  the  eclipse  of  1905  : 
such  a  long  duration  of  darkness  ;  a  locality  with  so  good  a 
promise  of  a  clear  sky  ;  such  a  high  altitude  for  the  Sun  above 
the  horizon  ;  and  a  locale  so  accessible  from  the  shores  of 

'  This  is  what  is  commonly  stated,  but  according  to  the  map  in  Oppolzer's 
Canon  der  Finstcrnisse,  the  central  line  does  not  touch  England,  but  passes 
a  certain  number  of  miles  to  the  S.  and  so  into  France. 


OBSERVATIONS    OF    ECLIPSES.  1 29 

England  as  was  Spain.  Finally,  it  may  be  stated  that  on 
October  7,  2135,  there  will  be  an  eclipse  the  central  line  of 
which  will  pass  over  the  middle  of  England. 

Speaking  generally,  total  eclipses  of  the  Sun  may  be  said  not 
to  vary  very  much  in  number  from  century  to  century,  but  the 
greater  facilities  for  travel  which  we  can  now  command,  com- 
pared with  the  limited  opportunities  possessed  by  our  ancestors, 
or  even  by  our  grandfathers,  make  the  subject  of  eclipses 
much  more  familiar  to  us  nowadays  than  was  formerly  the 
case  ;  and  the  eclipses  since  the  middle  of  the  igth  century, 
observed  as  they  have  been  in  many  parts  of  the  world  which 
used  to  be  more  or  less  inaccessible,  have  yielded  the  numerous 
and  important  disclosures  respecting  the  constitution  of  the 
Sun  which  have  been  mentioned  earlier  in  this  chapter. 

As  regards  the  question  of  instruments,  it  is  no  longer 
sufficient  to  be  content  with  simple  eye-observations  of  the 
visible  sights  offered  by  an  eclipse  to  persons  armed  with 
only  ordinary  telescopes.  Of  course  a  telescope  (which  need 
not  be  a  very  large  one)  is  necessary,  or,  at  least,  very  useful 
for  observing  the  outward  appearances  exhibited  during  the 
progress  of  a  solar  eclipse.  Indeed,  an  opera-glass,  or  even 
the  naked  eye,  suffices  to  disclose  many  interesting  features ;  but, 
to  perform  eclipse  observations  of  the  highest  value  in  the 
most  up-to-date  fashion,  a  good  deal  more  is  wanted  than  a 
mere  telescope.  Moreover,  the  astronomer  requires  the  active 
assistance  of  a  photographer  and  of  a  practical  chemist,  to  say 
nothing  of  an  outfit  of  clocks  and  of  time-keepers  to  manage 
them.  Accordingly,  the  impedimenta  of  a  fully  equipped 
eclipse  expedition  are  vastly  more  numerous,  more  heavy, 
more  bulky,  than  was  the  case  in  by-gone  days  ;  and  it  is  only 
the  modern  application  of  steam  1o  railways  and  ships  which 
enables  astronomers  of  the  2oth  century  to  do  the  work  which 
the  scientific  exigencies  of  the  century  demand. 

Even  with  the  facilities  here  referred  to,  it  will  easily  be 
understood  that  it  is  no  joke  to  organise  and  carry  to  a  success- 

9 


133  ECLIPSES. 

ful  issue  eclipse  expeditions  from  England  to  such  far-off 
localities  as  India,  or  Polynesia,  or  the  West  Indies,  though 
such  things  have  been  done  several  times  within  recent  years. 
When,  however,  English  astronomers  in  England  had,  in  1905, 
the  chance  of  a  total  eclipse  of  the  Sun  no  farther  off  than 
Spain,  perhaps  700  miles  away,  it  was  obvious  that  there  would 
be  a  rush  to  see  it,  which  would  not  have  occurred  if  it  had  been 
a  question  of  a  voyage  to  Java,  or  Tierra  del  Fuego.  Hence  it 
came  about  that  the  eclipse  of  1905,  already  mentioned,  had 
been  looked  forward  to  with  great  interest  by  vast  numbers  of 
English  people,  astronomers  and  non-astronomers.  These 
may  be  said  to  have  had  their  appetite  whetted  by  the  eclipse 
of  May  1900,  also  visible  as  near  to  England  as  Spain  and 
Portugal.  But  this  eclipse  was  under  the  important  disability 
that  its  duration  was  very  short,  only  i^  minutes — a  period  too 
brief  wherein  to  see  or  do  much.  On  the  other  hand,  the 
eclipse  of  1905  was  due  to  last  3^  minutes,  an  interval  to  be 
deemed  substantial,  seeing  that  under  no  circumstances,  as 
already  stated,  can  the  most  favourable  totality  last  for  more 
than  about  6  or  7  minutes.1 

Therefore  the  probabilities  were  that  large  numbers  would 
flock  to  Spain  from  England  (and,  for  the  matter  of  that, 
from  France  and  Germany)  to  see  the  eclipse  of  1905. 
Accordingly,  some  account  of  the  preparations  which  had 
to  be  made  (indeed  which  always  have  to  be  made  before 
total  eclipses)  will  probably  interest  the  reader. 

Preparations  began  much  further  back  than  a  few  months 
before  the  great  event.  Though  it  is  rather  the  fashion  to  run 
down  Spain  and  things  Spanish,  it  must  be  stated,  to  the  credit 
of  the  Spanish  Government,  that  more  than  4  years  in 
advance  did  the  Madrid  Observatory  begin  taking  steps  to 
prepare  for  the  eclipse,  first  by  the  issue  of  a  very  good  map  of 
the  path  of  the  central  line  across  Spain,  and  afterwards  by  the 
issue  of  additional  maps  and  a  pamphlet  of  suggestions  and 

1  Whitmell,  Monthly  Notices,  Royal  Astronomical  Society,  vol.  Ix.  p.  435. 


ORGANISATION    OF    ECLIPSE    PARTIES.  13! 

advice.  These  preliminary  documents  proved  most  useful  to 
the  English  Astronomical  Societies  and  private  individuals  who 
undertook  to  organise  the  necessary  travelling  arrangements. 

In  all  such  matters  there  are  certain  very  important  points 
to  be  handled,  to  which  all  others  must  be  subordinate.  First 
and  foremost  comes  the  question  of  probable  weather  at  possible 
observing  stations  situated  in  or  near  the  central  line.  Infor- 
mation as  to  this  had  to  be  sought  from  existing  records  already 
published  by  Spanish  meteorological  authorities.  These  were 
obtained,  consulted,  and  tabulated  with  the  following  general 
results. 

It  was  found  that  there  was  a  probability  of  fog  and  haze 
prevailing  at  the  end  of  August  on  the  N.  coast  of 
Spain,  at  or  near  the  actual  coast-line,  though  this  could  be 
evaded  by  journeying  50  miles  inland  by  roads  or  railways 
to  towns  without  hotel  accommodation.  Still  further  inland, 
especially  at  and  near  the  important  city  of  Burgos,  it 
was  found  that  eligible  positions  could  be  selected  for  ob- 
serving the  eclipse,  all  the  more  eligible  because,  Burgos 
being  at  a  considerable  elevation  above  the  sea,  a  fair  amount 
of  fresh  air  at  a  moderate  temperature  was  understood  to  be 
obtainable 

The  question  of  temperature  constituted  all  along  a  great 
difficulty  in  making  up  eclipse-observing  parties,  it  being  well 
known  that  the  summer  temperature  of  the  S.E.  of  Spain 
is  quite  tropical  in  its  character.  Next  after  the  question  of 
temperature  came  the  question  of  sleeping  accommodation, 
beds  and  bedding  to  the  taste  of  Mr.  and  Mrs.  John  Bull  being 
difficult  to  obtain,  indeed  almost  non-existent  in  Spain. 

When  the  eclipse  came  within  a  measurable  distance— that  is 
to  say,  about  a  year  and  a  half  before  the  appointed  day— the 
British  Astronomical  Association  nominated  a  special  committee 
to  consider  the  travelling  and  observing  arrangements  which  it 
was  expedient  to  make.  The  question  of  travelling  was  dealt 
with  first.  The  difficulties  which  it  was  known  would  have  to 


132  ECLIPSES. 

be  faced  in  respect  of  the  extreme  heat  and  the  general  lack  of* 
comfortable  sleeping  accommodation  led  the  Committee,  in  the 
first  instance,  to  contemplate  the  employment  of  a  large  ocean- 
going steamer,  which  should  land  parties  to  settle  themselves 
at  different  places  on  the  S.E.  coast,  with  Valencia  as  the 
permanent  headquarters  for  the  steamer,  for  a  week  or  more, 
making  use  of  the  steamer,  as  much  as  possible,  as  a  floating 
hotel. 

Several  steamship  companies  applied  to  one  and  all  refused 
to  negotiate  with  the  Committee  except  on  terms  and  conditions 
which  were  so  excessive  as  to  be  prohibitive.  The  con- 
templated grand  expedition  in  its  complete  form  had  then  to 
be  abandoned,  and  the  70  or  more  scientific  excursionists 
who  had  given  in  their  names  to  go  somewhere  or  other  were 
left  to  make  arrangements  for  themselves  as  best  they  could. 

The  redoubtable  Cook  then  came  upon  the  scene,  and  offered 
personally  to  conduct  parties  overland  through  France  to 
Burgos,  and,  partly  by  land  and  partly  by  sea,  to  the  Balearic 
Islands  via  Marseilles. 

The  Polytechnic  Institution  offered  to  organise  another  party 
from  London  to  Burgos  at  a  helter-skelter  pace  and  cheap 
fares.  Their  number  (20)  was  soon  made  up.  Besides  the 
foregoing  there  were  attempts  made,  with  more  or  less  (gener- 
ally less)  success,  to  get  up  detachments  for  Gijon,  on  the 
N.  coast  of  Spain,  for  Valencia  on  the  S.E.  coast,  and  for 
Philippeville  in  Algiers. 

The  merits  of  these  various  subsidiary  observing  centres 
generally  turned  on  the  facilities  available  for  local  travelling 
from  the  chief  centre  and  on  the  question  of  hotels  ;  for,  happily 
so  far  as  the  Mediterranean  portion  of  the  eclipse  area  was 
concerned,  there  was  never  any  serious  doubt  or  risk  about  fine 
weather  and  a  clear  sky  being  assured. 

Observations  of  eclipses  of  the  Sun  differ  from  all  other 
astronomical  observations  in  a  very  important  particular. 
Most  observations  are  performed  by  one  chief  observer  with  or 


ORGANISATION    OF    ECLIPSE    PARTIES.  133 

without  some  assistance  from  a  subordinate,  who  will  perform 
such  minor  duties  as  calling  out  or  writing  down  times  as 
indicated  by  a  clock,  or  opening  or  shutting  photographic 
shutters  and  slides.  An  ordinary  observer,  with  or  without  a 
little  help  from  a  junior,  can,  as  a  rule,  take  his  own  time  in 
performing  the  task  which  he  has  undertaken,  or  which  has 
been  allotted  to  him.  Things  are  quite  otherwise,  however, 
when  a  total  eclipse  of  the  Sun  is  in  question.  There  is  then 
no  opportunity  for  leisurely  work.  A  dozen  different  things 
have  to  be  performed,  or  looked  at,  practically  all  at  once — at 
any  rate,  within  the  compass  of  a  few  minutes,  which  seldom 
exceed  three  or  four  at  the  outside. 

A  well-disciplined  eclipse  observer  has,  therefore,  to  make 
up  his  mind,  not  only  that  he  cannot  see  everything  himself, 
but  that  he  can  hardly  hope  to  see  even  one-tenth  of  every- 
thing. The  work,  therefore,  calls  for  much  self-denial  on  the 
part  of  the  earnest  votary  of  science,  who  must  patiently 
resolve  to  concentrate  his  mind  on  some  one  or  two  special 
points,  whilst  his  next-door  neighbour  on  one  side  concentrates 
his  thoughts  on  a  third  or  fourth  special  point,  and  another 
neighbour  gives  his  mind  perhaps  to  a  fifth,  or  sixth,  special 
point  ;  and  so  all  the  expected  phenomena  are,  by  judicious 
pre-arrangement,  shared  out  amongst  the  different  members  of 
a  party  or  expedition. 

Before  every  eclipse  it  is  usual  for  the  members  of  a  party, 
especially  if  they  belong  to  some  public  or  State  Observatory,  to 
go  through  a  sort  of  military  rifle  and  aiming  drill,  to  practise 
what  they  will  have  to  perform  during  the  critical  brief  minutes 
of  totality,  and  to  make  sure  beforehand  that  each  understands 
his  own  duty  and  his  own  instrument,  etc.,  and  will  not 
trespass  upon  the  duties  of  his  coadjutors,  or  have  a  fiasco 
with  his  own  instruments  or  apparatus.  Prior  to  the  eclipse  of 
1900  the  Astronomer  Royal's  party  at  Greenwich  had  a  grand 
rehearsal,  which  was  afterwards  repeated  with  models  of  a 
sham  eclipse,  much  to  the  amusement  of  the  spectators,  at 


134  ECLIPSES. 

a  meeting  of  the  Royal  Astronomical  Society  at  Burlington 
House. 

Inspired  by  this  precedent,  one  day  in  July  1905,  the  Eclipse 
Committee  of  the  British  Astronomical  Association  gathered 
together  a  number  of  those  who  intended  to  observe  the  eclipse, 
and  carried  out  a  very  useful,  though  informal,  exchange  of 
ideas  as  to  what  observations  were  possible  with  the  instrumental 
appliances  at  the  command  of  each  with  a  view  of  avoiding  to 
some  degree,  by  pre-arrangement,  waste  of  time  and  waste  of 
labour  on  the  great  day.  And  some  of  those  who  were  posted 
up  in  the  intricacies  of  French  and  Spanish  railway  travelling, 
and  Spanish  hotel  life,  unfolded  their  experiences  for  the  benefit 
of  novices  present. 

As  regards  the  work  which  was  to  be  performed — that  is,  the 
observations  which  were  to  be  made — the  Eclipse  Committee 
just  named  entrusted  the  preparation  of  an  "agenda"  to 
Mr.  E.  W.  Maunder,  of  the  Royal  Observatory,  Greenwich,  and 
it  is  needless  to  add  that  the  work  was  well  and  judiciously 
done.  It  had  scarcely  been  accomplished  when  Mr.  Maunder 
had  to  resign  his  secretaryship  of  the  Eclipse  Committee  because 
the  Canadian  Government  had  honoured  him  with  an  invitation 
to  join  their  observing  party,  which  was  going  to  the  far-off 
locality  of  Labrador,  and  which,  therefore,  rendered  it  necessary 
for  him  to  leave  England  some  weeks  before  the  Spanish  parties 
did  so. 

At  well-nigh  the  eleventh  hour,  when  all  other  attempts  to 
negotiate  an  expedition,  wholly  or  almost  wholly,  by  sea,  had 
failed,  it  was  discovered  that  the  P.  &  O.  Mail  steamer  leaving 
Tilbury  on  August  25  was  due  to  cross  the  line  of  central 
eclipse,  or  totality  as  it  is  generally  called,  on  the  very  day, 
and  almost  at  the  very  hour,  of  the  eclipse,  and  negotiations 
were  entered  into  with  the  Company  with  a  view  of  arranging 
that  the  ship  should  heave-to  for  two  or  three  hours  to  enable 
the  passengers  ta  have  a  leisurely  view  of  the  phenomenon.  So 
soon  as  this  decision  was  arrived  at  it  was  communicated  to  all 


PREPARATIONS    FOR    THE    ECLIPSE    CF    1905.  135 

the  members  of  the  British  Astronomical  Association,  and 
others  who  had  desired  to  see  the  eclipse  without  incurring 
the  many  disagreeables  of  a  land  journey  across  France  and 
Spain  during  the  hot  days  of  August.  Thanks  to  the  officials  of 
the  P.  &  O.  Company,  the  details  were  soon  worked  out. 

This  review  of  the  situation  will  enable  the  reader  to  under- 
stand something  of  the  nature  of  the  preliminary  matters  which 
had  to  be  handled  ;  but  my  statement  of  them  is  very  far  from 
being  exhaustive,  for  I  have  limited  myself  to  matters  affecting 
those  who  were  going  abroad  from  England. 

I  have  said  nothing  about  what  the  Americans  proposed  to 
do,  and  the  Americans  always  carry  out  their  scientific  expedi- 
tions in  good  style,  and  with  thoroughness  ;  nor  have  I  said 
anything  about  French  or  German  efforts.  France  has  an 
Astronomical  Association,  run  very  much  on  the  same  lines  as 
the  English  Association,  and  it  was  at  one  time  hoped  that 
some  sort  of  organised  co-operation  might  have  been  arrived  at 
between  the  two  bodies  ;  but  this  did  not  come  about,  chiefly 
because  the  travelling  necessities  of  the  two  nations  were 
diverse,  the  English  having  to  cross  the  water  to  get  to  Spain, 
whilst  the  French  were  already  next  door. 

Since  the  eventful  month  of  December  in  the  eventful  year 
1870,  when  the  distinguished  French  astronomer,  Janssen, 
escaped  from  beleaguered  Paris  in  a  balloon  in  order  to  observe 
the  total  eclipse  of  the  Sun  of  December  22,  1870,  there  have 
been  many  expeditions  to  all  parts  of  the  world  to  observe 
occurrences  of  the  same  phenomenon.  So  far  as  I  can  re- 
member, there  has  never  been  an  instance,  till  the  year  1905, 
of  an  expedition  of  astronomers  and  astronomically-minded 
people  having  been  avowedly  organised  to  observe  an  eclipse 
at  a  "  station  "  on  the  high  seas. 

The  nearest  approach  to  this  would  seem  to  have  been  the 
stoppage  for  an  hour  or  two  in  mid-Atlantic,  on  May  29,  1900, 
of  the  ss.  Austral,  of  the  Orient  Line,  on  its  outward  voyage  to 
Australia  in  order  that  its  passengers  might  view  the  total 


136  ECLIPSES. 

phase  of  that  day.  There  was,  however,  no  set  purpose  on 
the  part  of  the  steamship  company  to  provide  this  special  show 
for  the  benefit  of  the  passengers.  The  episode  was  contrived 
by  Colonel  Markwick,  R.A.,  F.R.A.S.,  who  had  obtained  an 
assurance  that  the  steamer  would  cross  the  eclipse  line  at  the 
right  place  and  time.  The  eclipse  of  April  17,  1912,  was  by  an 
arrangement  with  the  captain  viewed  by  Mr.  W.  B.  Gibbs, 
F.R.A.S.,  on  board  the  Union  Castle  s.s.  Balmoral  Castle  off 
the  coast  of  Portugal. 

Nor  do  I  think  there  was  any  set  purpose  in  the  mind  of 
the  captain  of  the  French  man-of-war  Le  Comte  tfArtois, 
who,  in  the  middle  of  the  i8th  century,  observed  at  sea  the 
eclipse  of  February  9,  1766.  Possibly,  however,  it  was  by 
design  that  the  Spanish  Admiral,  Don  Antonio  Ulloa,  saw  the 
total  eclipse  of  June  24,  1778,  at  sea,  when  passing  from  the 
Azores  to  Cape  St.  Vincent.  His  observations,  published  in 
the  Philosophical  Transactions,  1779,  considering  their  early 
date,  are  extremely  interesting. 

The  land  observations  in  1905  call  for  no  special  notice  in 
this  place  as  regards  the  personal  adventures  of  the  observers 
who  chose  terra  firma  in  Spain  for  their  work,  but  the  fortunes 
of  the  sea-going  party,  of  whom  I  was  one,  are  worth  a  brief 
mention  because  of  their  novelty.  This  section  of  observers 
took  ship  at  Tilbury  on  board  the  P.  &  O.  steamer  Arcadia, 
Captain  Cubitt.  After  an  uneventful  voyage,  only  varied  by 
landing  for  a  few  hours  at  Gibraltar,  we  arrived  in  the  forenoon 
of  the  eventful  day,  August  30,  at  the  exact  spot  in  the 
Mediterranean,  not  far  from  the  Balearic  Isles,  in  the  precise 
latitude  and  longitude  which  it  was  calculated  would  put  us  on 
the  central  line  of  the  eclipse  ;  and  so  it  did,  and  we  saw 
everything  most  successfully,  thanks  to  Captain  Cubitt's  kind 
and  painstaking  co-operation. 

Before  the  eclipse  we  knew  that  there  was  one  special 
problem  to  be  solved  which  dominated  all  others  :  could  we 
fjnd  the  proper  position,  and,  having  found  it,  CQuld  we  keep  it 


FIGS.   149-151 


PLATE    XLIV. 


No.  i. — ii  h.  46  m.  scfs.  G.M.T. 


No.  3. — 12  h.  ii  m. 

The  Eclipse  of  the  Sun,  April  17,  1912,  as  seen  at  Bournemouth. 

(E.   W.  Barlow,  photo.} 

[(Notice  that  2  and  3  represent  crescents  of  the  Sun  of  the  same  form, 
but  a  different  part  of  the  Sun  is  exposed  to  view.) 


136] 


FIGS.  152-153 


PLATE    XLV. 


snd  stage. 

Total  Eclipse  of  the  Moon,  Jan.  28,  1888. 


FIGS.   154-155 


PLATE   XLVI. 


1366] 


4th  stage. 

Total  Eclipse  of  the  Moon,  Jan.  28,  1888. 


PLATE    XLVII. 


5th  stage. 

Total  Eclipse  of  the  Moon,  Jan.  28,  1888. 
FIGS.  157-160 


Oceultation  of  Jupiter  by  the  Moon,  Aug.  12,  1892  (W.  H.  Pickering}. 

[137 


SKETCHING  THE  CORONA. 


137 


for  two  hours,  and  especially  for  the  10  minutes  which  would 
include  the  critical  events  of  the  eclipse  ;  and  would  the  ship 
be  steady  enough  on  the  water  to  enable  the  necessary  observa- 
tions to  be  made  ?  Everything  happened  just  as  was  wanted, 


Fig.  161.— The  Corona,  Aug.  8,  1896,  as  sketched  by 
E.  J.  Stone's  system. 

the  most  remarkable  thing  of  all  being  the  steadiness  and  the 
fixity  of  the  ship.  This  last  was  accomplished  by  the  ship 
being  kept  moving  at  the  calculated  speed  of  three  knots  an 
hour,  which  neutralised  the  strong  set  of  the  current  in  the 
reverse  direction.  All  of  us,  or  most  of  us,  were  able  to 


138  ECLIPSES. 

observe  the  usual  concomitants  of  total  eclipses  of  the  Sun  ;  but 
the  only  feature  needing  notice  here  was  the  lack  of  darkness 
of  the  usual  intensity,  or  anything  like  it.  Probably  that  was 
the  result  of  our  viewing  the  eclipse  with  nothing  but  water 
surrounding  our  place  of  observation. 

Fig.  161  represents  a  diagram  devised  by  E.  J.  Stone  for 
noting  down  in  haste  the  streamers,  etc.,  visible  in  a  total 
Eclipse  of  the  Sun.  The  diagram  is  an  instance  of  its  actual 
use  by  Stone  on  the  occasion  of  the  Total  Eclipse  of  the  Sun 
of  August  9,  1896.  The  diagram,  however,  may  be  usefully 
employed  for  other  purposes  if  copies  of  it,  printed  on  cards, 
are  kept  for  use  with  a  telescope.  In  the  case  of  occultations 
of  stars  by  the  Moon  the  points  on  the  lunar  limb,  where  the 
stars  will  disappear  and  reappear,  may  be  marked  before- 
hand ;  and  so  time  may  be  saved,  and  the  stages  of  the 
phenomenon  not  lost  because  the  observer  is  not  sure  where 
to  look  for  the  stars.  Other  uses  for  such  cards  will  present 
themselves  to  an  observer  from  time  to  time  ;  for  instance, 
in  observing  the  Sun  or  double  stars  they  will  come  in  very 
handy. 

We  will  now  consider  the  eclipses  of  the  Moon  in  some 
further  detail.  It  may  be  said,  generally,  that  whilst,  for 
reasons  mentioned  in  an  earlier  part  of  this  chapter,  these 
eclipses  are  more  often  visible  to  those  who  choose  to  look  for 
them  than  eclipses  of  the  Sun,  yet  they  kindle  much  less 
enthusiasm  than  eclipses  of  the  Sun,  partly  for  the  reason,  no 
doubt,  that  they  are  devoid  of  sensational  features  of  display 
and  points  of  general  interest.  Indeed,  almost  the  only  matter 
which  an  intending  observer  of  a  total  eclipse  of  the  Moon  has 
to  put  down  on  his  agenda  is  the  question,  What  will  be  the 
aspect  of  the  Moon  when  most  deeply  immersed  in  the  Earth's 
shadow?  will  it  be  visible  at  all?  or  will  it  be  invisible?  or,  if 
visible,  how  will  it  look  ?  Of  course  one  may  say  that,  by  rights, 
it  ought  to  be  altogether  invisible,  and  so  very  frequently  it  is  ; 


PLATE  XLVIII 


TOTAL    ECLIPSE    OF    THK    MOON. 

1867. 


(Tempel) 


ECLIPSES    OF    THE    MOON.  139 

but,  on  the  other  hand,  it  is  frequently  visible  between  the 
extremes  of  showing  traces  of  its  existence,  and  showing  its 
whole  disc  quite  prominently  of  a  more  or  less  bright  coppery 
colour.  There  are  no  discoverable  laws  which  regulate  these, 
variations,  and  it  can  only  be  said,  very  vaguely,  that  they 
depend  upon  the  variable  condition  of  the  Earth's  atmosphere. 
If  the  portion  of  the  atmosphere  through  which  it  so  happens 
that  the  Sun's  rays  have  to  pass  are  highly  saturated  with  aqueous 
vapour,  the  red  rays  will  be  transmitted  freely,  and  the  Moon's 
surface  will  be  highly  illuminated.  If,  on  the  other  hand, 
aqueous  vapour  is  deficient,  the  red  rays  will  be  more  or  less 
absorbed,  and,  as  the  blue  will  predominate,  the  illumination 
will  be  extinguished. 

When,  on  the  occasion  of  a  total  eclipse,  some  parts  of  the 
Moon's  disc  are  visible  and  others  invisible,  the  variation 
may  be  considered  due  to  the  prevalence  of  moisture  in  some 
parts  of  the  atmosphere  through  which  the  Moon's  rays  reach 
us,  and  its  absence  in  other  parts,  thus  emphasising  the  dis- 
tinctions just  pointed  out.  It  is  right  to  add  that,  by  various 
competent  authorities,  the  foregoing  explanations  are  deemed 
unsatisfactory  ;  but  nothing  better  has  as  yet  been  offered  in 
substitution. 

There  have  been  total  eclipses  of  the  Moon  recorded  which 
have  played  a  part  in  certain  mundane  events.  An  experience 
which  befel  Christopher  Columbus  is  a  case  in  point.  In 
February  1504  Columbus  found  himself  at  the  island  of 
Jamaica  in  great  straits  for  want  of  provisions,  which  the 
islanders  refused  to  provide,  and  he  was  therefore  at  his  wits' 
end  to  know  what  to  do.  What  followed  shall  now  be  told  in 
the  words  of  his  son  : — • 

"  He  bethought  himself  that,  within  three  days,  there  would 
be  an  eclipse  of  the  Moon  in  the  first  part  of  the  night  ;  and 
then  sends  an  Indian  of  Hispaniola  with  us  to  call  the  principal 
Indians  of  that  province,  saying  he  would  talk  with  them  about 
a  matter  of  concern.  Being  come  that  day  before  the  eclipse  was, 


140  ECLIPSES. 

he  ordered  the  interpreter  to  tell  them  that  we  were  Christians 
and  believed  in  God,  who  dwelt  in  heaven  and  took  care  of  the 
good  and  punished  the  wicked  .  .  .  that,  as  for  the  Indians, 
seeing  how  negligent  they  were  in  bringing  provisions  for  our 
commodities,  He  was  angry  with  them,  and  had  decreed  to 
punish  them  with  plague  and  famine  ;  which  because,  perhaps, 
they  would  not  believe,  God  had  appointed  to  give  them  a 
manifest  token  of  it  in  the  heaven,  that  they  might  plainly 
know  the  punishment  was  to  come  from  Him.  Therefore,  he 
bid  them  observe  that  night  when  the  Moon  appeared,  and 
they  should  see  her  rise  angry  and  of  a  bloody  hue,  to  denote 
the  mischief  God  intended  should  fall  on  them.  Having  said 
this  to  them,  the  Indians  went  away,  some  afraid  and  others 
looking  upon  it  as  an  idle  story  ;  but  the  eclipse,  beginning  as 
the  Moon  was  rising,  and  increasing  the  higher  she  was,  the 
Indians  took  notice  of  it,  and  were  so  frightened  that  they  came 
running  from  all  parts  loaded  with  provisions,  crying  and 
lamenting,  and  prayed  the  admiral  by  all  means  to  intercede 
with  God  for  them,  that  He  might  not  make  them  feel  the 
effects  of  His  wrath,  and  promising  for  the  future  carefully  to 
bring  him  all  he  wanted.  The  admiral  said  he  would  speak 
with  God,  and  shut  himself  up  while  the  eclipse  lasted,  they 
still  crying  out  to  him  to  assist  them  ;  and  when  the  admiral 
saw  the  eclipse  began  to  go  off,  and  the  Moon  would  soon 
shine,  he  came  out  of  his  cabin,  saying  he  had  prayed  to  his 
God  for  them,  and  promised  Him  in  their  names  they  would  be 
good  for  the  future,  and  use  the  Christians  well,  bringing  them 
provisions  and  other  necessaries ;  and  that  therefore  God 
forgave  them,  and  as  a  token  of  it  they  should  see  the  angriness 
and  bloody  colour  of  the  Moon  would  go  off.  This  proving  so, 
just  as  he  spoke  it,  they  gave  the  admiral  many  thanks,  and 
praised  God,  continuing  so  till  the  eclipse  was  quite  passed. 
From  that  time  forward  they  always  took  care  to  provide  all 
that  was  necessary,  ever  praising  the  God  of  the  Christians  ; 
for  they  believed  the  eclipses  they  had  seen  at  other  times  had 
denoted  mischiefs  to  befall  them  ;  and,  being  ignorant  of  the 
cause  of  them,  and  that  they  happened  at  certain  times,  not 
believing  it  possible  to  know  on  earth  what  was  to  happen  in 
the  heavens,  they  certainly  concluded  the  God  of  the  Christians 
had  revealed  it  to  the  admiral."  l 

1  See  Pinkerton,  Voyages,  vol.  xii.  p.  148. 


EXTERNAL 
CONTACT 


11 

INTERNAL 
CONTACT 

in 


Fig.  163.— Phases  of  the  Transit  of  an  Inferior  Planet. 

141 


142  ECLIPSES. 

This  story  records  alike  the  credulity  of  the  natives  and  the 
mingled  piety  and  astuteness  of  the  great  navigator.  It  might 
well  be  regarded  as  an  example  of  that  worst  of  all  frauds,  a 
"  pious  fraud." 

The  most  recent  instance  of  the  utilisation  of  a  total  eclipse 
of  the  Moon  occurred  on  December  16,  1899.  What  happened 
is  thus  described  by  the  Times  correspondent  with  Lord 
Methuen's  army  at  the  Modder  River  in  South  Africa  : — 

"The  Full  Moon  has  prevented  satisfactory  search-light 
communication  lately,  but  Kimberley  took  advantage  eagerly 
of  the  eclipse  last  night  to  get  important  despatches  through." 


Akin  to  eclipses  of  the  Sun  are  two  astronomical  phenomena 
which  go  by  the  names  of  "  Transits "  and  "  Occultations." 
They  are  entirely  identical  in  principle  with  solar  eclipses,  but 
involve  other  celestial  bodies. 

In  a  previous  chapter  it  has  been  pointed  out  that  the  two 
Inferior  Planets,  Mercury  and  Venus,  are  constantly  passing 
round  the  Sun,  and  between  the  Earth  and  the  Sun  ;  and  that 
when  the  Earth,  Planet,  and  Sun  are  in  an  exact  straight  line 
the  planet,  whichever  it  be,  will  be  seen  projected  on  the 
Sun's  disc.  On  such  occasions  (which  are  not  very  often 
in  the  case  of  Mercury  and  very  rare  in  the  case  of  Venus) 
the  planet  presents  the  appearance  of  a  sharply  defined  round 
black  spot.  The  occurrence  of  such  a  transit  offers  an 
opportunity  for  determining  the  distance  of  the  Earth  from 
the  Sun.  Mercury  is  not  so  suitable  for  this  purpose  as 
Venus,  because  of  its  proximity  to  the  Sun;  but  Venus 
has  frequently  been  used  for  obtaining  a  solution  of  this 
problem.  The  actual  modus  operandi  is  somewhat  complex 
and  beyond  the  scope  of  this  volume.  Suffice  it,  then,  to  say 
that  it  depends  for  its  success  on  the  skill  and  care  with  which 
observers  at  remote  distances  from  one  another  on  the  Earth 


OCCULTATIONS.  143 

can  determine  micrometrically  the  exact  points  on  the  Sun,  as 
viewed  from  northern  and  southern  stations  on  the  Earth,  at 
which  the  planet  appears  to  enter  and  to  quit  the  Sun's  disc  in 
the  course  of  its  passage  across  the  Sun.  By  the  application  of 
trigonometry  (or  mathematics  applied  to  angles)  the  distance 
desired  to  be  known  can  be  calculated. 

The  satellites  of  Jupiter  also  perform  transits  over  their 
primary's  disc  the  observation  of  which,  though  of  no  important 
scientific  value,  furnish  interesting  spectacles  from  a  star-gazing 
standpoint.  They  also  suffer  eclipse  by  passing  behind  the 
planet.  Both  these  Jovian  phenomena  are  dealt  with  in  the 
various  almanacs  which  embrace  scientific  events. 

An  Occultation,  in  the  literal  meaning  of  the  word,  is  the 
covering  over  of  one  celestial  body  by  another.  Accordingly, 
in  a  dictionary  ^ense,  when  a  total  eclipse  of  the  Sun  takes  place 
the  Sun  is  occulted  by  the  Moon  ;  but  the  word  "  Occultation  "  is 
by  usage  confined  to  cases  where  the  Moon  hides  a  planet  or 
a  star,  or  one  planet  hides  another  planet  or  a  star.  Occulta- 
tions  by  the  Moon  of  stars  which  lie  in  its  path  across  the 
heavens  are  common  enough  and  occur  daily.  Sometimes  the 
Moon  occults  a  planet,  which  naturally  intensifies  the  interest 
attaching  to  the  event.  In  the  case  of  the  larger  planets  and 
stars  brighter  than  the  6th  mag.  anticipations  of  the  occurrence 
will  be  found  stated  in  the  Nautical  Almanac  whence  the 
information  is  copied  into  Whitaker's  Almanac  and  other 
almanacs.  When  an  Occultation  occurs  between  the  time  of 
New  Moon  and  First  Quarter  the  effect  is  very  striking,  because 
the  star  occulted  is  suddenly  extinguished  at  a  point  where  the 
sky  appears  uniformly  dark,  and  where  there  seems  no  sufficient 
reason  for  anything  to  interfere  suddenly  with  the  star.  Occul- 
tations  may  be  said  to  be  celestial  phenomena  specially  within 
the  reach  of  amateurs  because,  when  they  take  place  with  the 
Moon  young  in  age,  they  happen  at  conveniently  early  hours  in 
the  evening,  and  are  within  the  reach  of  telescopes  however 
small. 


CHAPTER  IX. 
COMETS. 

Always  objects  of  popular  interest. — Very  numerous. — Telescopic  comets. 
— Great  comets  visible  to  the  naked  eye. — Changes  in  the  appearance 
of  a  comet  after  its  first  discovery. — Often  easily  mistaken  for  a 
nebula. — Usual  changes  exhibited  by  a  telescopic  comet. — Become 
visible  as  they  approach  the  Sun. — What  is  a  comet's  tail  ? — Where 
does  it  come  from  ? — Why  do  some  comets  have  tails  and  not  others  ? 
— These  questions  difficult  to  answer. — Sir  J .  HerscheVs  opinion. — 
General  account  of  tails. — Some  tails  probably  cylindrical. — Bre- 
dichen's  Types  of  tails. — The  "Light-pressure"  theory. — Orbits  of 
comets. — Periodical  comets. — Celebrated  comets. — Some  statistics. 

IT  may  safely  be  said  that  the  remarkable  objects  to  be  dealt 
with  in  the  present  chapter  have  had  a  good  deal  to  do  with  the 
recent  spread  of  a  taste  for  astronomy,  assisted  by  the  increased 
space  devoted  to  scientific  subjects  by  the  ordinary  newspaper 
press,  and  by  the  liberal  subventions  granted  in  the  United 
States,  especially  during  the  last  30  years,  by  wealthy  men 
there  for  the  establishment  and  endowment  of  astronomical 
observatories. 

I  name  the  period  of  30  years  because  that  takes  us  back  to 
the  "great  comet  of  1882,"  which  attracted  world-wide  atten- 
tion, much  more  I  think  than  did  the  "great  comets"  of  1858 
and  1 86 1,  which  were  in  all  respects  finer  objects  than  the 
comet  of  1882.  All  these  will  require  notice  further  on.  For 
the  present  I  must  start  with  some  much  less  attractive  details, 
the  true  understanding  of  which  is  essential  if  we  would  get  a 
clear  and  satisfactory  grip  of  this  branch  of  astronomy. 


CLASSIFICATION  of  COMETS,  145 

Comets  may  be  said  generally  to  range  themselves  in  two 
classes  :  very  small  ones,  seldom  if  ever  visible  to  the  naked 
eye,  and  large  ones  easily  visible  to  the  naked  eye,  and  always 
exhibiting  tails  the  length  of  which  may  vary  between  two  or 
three  diameters  of  the  Moon  and  half  the  extent  of  the  visible 
sky.  The  last-named  sort  of  comet  appears  only  at  long  inter- 
vals of  time,  but  a  naked-eye  comet  with  a  tail  two  or  three 


Nov.  it.  Nov.  15. 

Figs.  164-165.— Brooks's  Comet  of  1898.  (X.) 

degrees  long  may  be  said  to  present  itself  every  two  or  three  or 
half  a  dozen  years. 

Here  we  have  to  face,  at  the  outset,  a  popular  view  of  things 
which  altogether  fails  to  accommodate  itself  to  the  superior 
knowledge  of  the  professed  astronomer.  Ask  the  first  person 
you  meet  the  question,  "What  is  a  Comet?"  and  the  answer 
will  always  be  something  like  this  :  "  A  celestial  object  which 
10 


146  COMETS. 

appears  unexpectedly  and  has  a  tail."  Such  an  explanation  and 
such  a  limited  definition  totally  fail  to  represent  the  facts  of  the 
case  as  brought  home  to  the  astronomer  working  with  a  duly 
equipped  telescope.  He  would  tell  us  that,  in  the  course  of  two 
or  three  years,  he  had  seen  probably  at  least  half  a  dozen 
comets,  none  of  them  visible  to  the  naked  eye,  and  none  of 
them  possessed  of  a  tail.  In  point  of  fact,  it  may  be  stated 
broadly  that,  in  the  course  of  a  generation,  dozens  of  comets 
come  within  our  reach,  most  of  them  very  diminutive  in  size 
and  rarely  having  tails.  Such  comets  are  designated  in 
astronomical  parlance  as  "  telescopic  comets,"  though  it  occa- 
sionally happens  that  here  and  there  one,  some  weeks  or  months 
after  its  first  discovery,  draws  nearer  to  the  Earth,  increases 
greatly  in  size,  puts  forth  a  tail,  and  becomes  to  the  man  in  the 
street  alone  worthy  of  the  title  of  "comet." 

Donati's  Comet  of  1858,  universally  known  as  the  "great 
comet "  of  that  year,  was  the  one  within  my  own  personal 
recollection  which  in  the  most  striking  manner  best  illustrates 
what  I  have  just  said.  Discovered  by  Donati  at  Florence  on 
June  2,  1858,  I  first  saw  it  in  a  7^-inch  refractor  in  August  of 
that  year.  On  one  evening  in  the  first  week  in  September  I 
could  just  manage  to  see  it  in  a  portable  3-inch  telescope.  It 
then  gradually  increased  in  size,  and  on  October  5  had  become 
one  of  the  largest  and  most  magnificent  comets  on  record,  not 
quite  so  much  from  the  length  of  its  tail  (though  that  extended 
to  about  50°)  as  from  the  wide,  fan-like  expanse  of  the  tail,  and 
its  great  brightness. 

I   have   cited   Donati's   Comet   as   illustrative,   albeit  in   an 
extreme  degree,  of  the  changes  which  telescopic  comets  often 
undergo,  but  the  ordinary  comet  of  this  class  occupies  a  much , 
more  humble  position  in  the  ken  of  the  astronomer. 

Whether  such  an  object  is  found  as  the  result  of  systematic 
search  for  comets  or  is  picked  up  by  chance  in  moving  a 
telescope  about  in  the  sky,  it  will  usually,  when  first  glimpsed, 
present  the  appearance  of  a  little  tiny,  cloudy  patch  which  may 


COMET    HUNTING. 


M7 


or  may  not  have  a  sharp,  star-like  centre.     Even  when  found 

and  presenting  such  an  aspect,  the  fact  of  its  being  truly  a  comet 

cannot  at  first  sight  be  known  for  a  certainty,  for  there  are 

many  nebulae  and  small  clusters  of  small  stars  which  can  be  at 

first  sight,  and  indeed  often  have  been,  regarded  as  comets,  and 

been   publicly  announced   as  such.     The  discreet  astronomer 

who  is  jealous  of  his  reputation  does  not  rush  at  once  to  the 

nearest  telegraph  office 

or  newspaper  office  and 

announce  his  discovery 

of  a  comet.    He  watches 

for  a  few  hours    to  see 

whether    the   object 

which  he  is  scrutinising 

is    stationary   or    in 

motion  with  respect  to 

the  neighbouring  stars. 

It     generally     happens 

that  three  or  four  hours 

will    enable   him    to 

answer     this     question 

one  way  or   the  other, 

but  it  frequently  occurs 

that  the  sudden  arrival 

of  clouds  shuts  out  the 

object     under    scrutiny 

too   soon   after  its  dis- 


Fig.  168.— Diagram  to  illustrate  the 
Recognition  of  a  Comet  as  distin- 
guished from  a  Nebula. 


covery  for  its  motion,  if  any,  to  be  ascertained,  and  the 
observer  who  thinks  and  hopes  he  has  found  a  new  comet 
has  to  wait  till  the  following  night  before  he  can  safely 
announce  his  success. 

What  I  may  call  an  ordinary  telescopic  comet  usually  passes 
through  the  following  stages  of  developement  :  when  first  found 
it  is  a  mere  luminous  patch,  in  or  near  the  centre  of  which  a 
slight  concentration  of  light  either  is  seen  at  the  very  first,  or 


148  COMETS. 

after  an  interval  developes.  This,  when  it  acquires  something 
like  a  distinct  central  brightness,  becomes  known  as  the 
"nucleus."  The  general  size  of  the  comet  and  its  brilliancy 
increase,  supposing  that  the  comet  is  approaching  both  the 
Earth  and  the  Sun  :  the  hazy,  nebulous  matter  around  the 
nucleus  becomes  broader  and  brighter,  and  is  then  spoken  of 
as  the  "  coma."  That  may  be  the  end  of  the  developement,  but 
very  likely  the  coma  will  go  on  expanding  in  one  direction, 
and,  after  giving  the  whole  object  an  elongated  or  oval 
appearance,  the  elongation  will  still  go  on  and  become 
eventually  a  real  tail.  These  transformations  occur  during 
the  gradual  approach  of  the  comet  to  the  Sun,  which  will 
generally  be  the  same  as  saying  its  gradual  approach  to  the 
Earth.  Here  comes  in  the  question,  What  will  be  the  time  of 
day,  or  rather  of  night,  when  the  comet  will  be  visible  ?  This 
depends  on  circumstances  which  vary  in  the  case  of  each 
successive  comet. 

Bearing  in  mind  that,  so  far  as  we  on  the  Earth  are  concerned, 
comets  only  as  a  rule  become  visible  when  approaching  the 
Sun,  it  may  be  stated  as  something  like  a  general  rule  that, 
when  a  comet  is  discovered  in  the  evening  twilight,  it  will 
gradually  become  more  and  more  immersed  in  the  twilight 
until  it  is  lost  in  the  rays  of  the  setting  Sun.  After  an  interval 
of  a  few  days,  or  two  or  three  or  more  weeks,  it  will  reappear  on 
the  other  side  of  the  Sun  in  the  morning  twilight,  and  gradually 
recede  from  the  Sun  until  it  becomes  lost  either  in  broad  day- 
light, or,  if  its  path  takes  it  amongst  the  stars  with  a  dark  back- 
ground, it  will  be  lost  to  view  owing  to  its  continuous  diminution 
of  apparent  size  due  to  its  increasing  distance  from  the  Sun  and 
the  Earth  alike. 

The  foregoing  account  of  what  may  be  called  the  rise  and 
fall  of  a  comet,  so  far  as  its  career  from  a  terrestrial  point 
of  view  is  concerned,  will  suffice  to  convey  a  general  notion 
of  what  happens  to  these  bodies  ;  but,  of  course,  particular 
comets,  by  reason  of  their  notorious  vagaries  in  the  heavens, 


TELESCOPIC   COMETS.  149 

may  come  and  go  without  conforming  to  the  stages  of  history 
set  forth  above.  For  instance,  it  often  happens  that  a  comet 
is  seen  for  the  first  time  when  its  visible  career,  so  far  as  we 
are  concerned,  is  coming  to  an  end  by  reason  of  the  fact  that 
its  nearest  approach  to  the  Earth  and  to  the  Sun  happened 
some  weeks  previously,  when  no  one  saw  it,  and  that  when  it 
was  first  seen  it  was  well  on  its  way  on  its  return  journey  to 
the  unknown  realms  from  which  it  came. 


Fig.  167. — Telescopic  Comet         Fig.  163. — Telescopic  Comet 
without  a  Nucleus.  with  a  Nucleus. 

The  subject  of  cometary  astronomy  is  such  a  very  large  one 
that  it  is  not  easy  to  know  where  to  draw  the  line  as  regards 
going  into  details.  The  changes  which  the  small  telescopic 
comets  usually  undergo  require,  for  their  proper  study,  tele- 
scopes of  considerable  power,  and  it  is  doubtful  whether  these 
changes  appeal  to  the  general  reader  or  popular  student.  It  is 
far  otherwise,  however,  with  the  tails  of  comets.  The  recorded 
varieties  of  tail  and  the  changes  which  have  been  noted  in 
the  tails  of  particular  comets  open  up  a  large  field  both  for 


150  COMETS. 

descriptive  writing  and  for  speculation.  It  must  suffice,  how- 
ever, here  to  state  a  few  general  outlines. 

Three  questions  frequently  asked  are  :  "  What  is  a  comet's 
tail  made  of?"  "Where  does  it  come  from?"  and  "Why  do 
some  comets  have  tails  and  not  others  ?" 

It  must  be  confessed  that  no  very  satisfactory  answers  can 
be  given  to  any  one  of  these  three  questions. 

The  first,  especially,  is  an  inscrutable  one,  and  a  remark  made 
by  the  late  Sir  John  Herschel,  some  three-fourths  of  a  century 
ago,  may  be  cited  as  an  indirect  indication  of  the  uncertainties 
which  confront  us.  He  said,  in  a  famous  passage,  that  the 
tails  of  comets  probably,  as  a  rule,  only  weigh  a  few  ounces  ! 
This  statement  may  sound,  and  perhaps  is,  fanciful  ;  but  it  is 
hard  to  disprove  it,  and  it  is  equally  difficult  to  prove  it,  and  a 
contented  confession  of  agnosticism  is  perhaps  the  safest 
attitude  to  assume. 

The  second  question,  "  Where  does  the  tail  of  a  comet  come 
from  ?"  is  a  little  more  easy  to  deal  with,  because  we  have  some 
evidence  of  our  eyes,  which  counts  for  something  in  this  con- 
nection. Whilst  in  a  certain  number  of  cases  it  may  be  said, 
with  Topsy,  that  the  tails  simply  "  grow "  by  visible  expansion 
from  the  comet,  yet  there  are  not  a  few  well-established  cases 
in  which  a  tail  has  been  seen  to  emanate  from  the  bright 
central  head  of  a  comet  precisely  as  a  jet  of  water  may  be  seen 
to  be  thrown  up  from  the  mouth  of  a  fountain.  The  third  comet 
of  1862,  as  sketched  by  Professor  Challis,  of  Cambridge,  was  a 
remarkable  instance  of  what  may  be  called  the  jet  origin  of 
a  comet's  tail  ;  but  there  are  many  other  instances  on  record. 
The  natural  idea  which  the  observation  of  a  comet  developing 
a  tail  from  its  nucleus  suggests  is  that  the  nucleus  is  a  source 
of  radiant,  luminous  matter  which  is  thrown  up  in  the  fashion  of 
an  Iceland  geyser.  This  is  how  the  matter  may  be  said  to 
come  home  to  the  eye  of  a  spectator  ;  but  the  difficulty  is  to 
realise  how  such  a  vast  mass  of  luminous  matter  can  be  pro- 
duced in  or  from  the  head  of  a  comet,  bearing  in  mind  the 


FIGS.  169-170 


PLATE    XLIX. 


"8 


»    3 
1    S 


150] 


FIG.   171 


PLATE   L. 


Encke's  Comet,  Sept.  22,  1848. 

(As  seen  at  the  Hartwell  Observatory.) 


THE    TAILS    OF   COMETS.  151 

evidence  we  possess  of  the  ethereal  character  of  these  bodies, 
and  their  lack  of  solid  substance  and  weight.  On  this  question 
of  lack  of  mass  it  will  be  necessary,  and  more  convenient,  to 
say  something  later  on. 

The  question  as  to  why  some  comets  have  tails  and  not 
others  is  another  of  those  points  connected  with  cometary 
astronomy  which  is  inscrutable.  Speaking  generally,  it  may  be 
said  that  very  small  comets  have  no  tails,  and  that  very  large 
comets  always  have  tails.  This,  however,  brings  us  no  nearer 
to  a  solution  of  the  question.  At  any  rate,  it  may  certainly 
be  affirmed  that  very  small  comets  which  are  no  brighter  than 
the  stars  of  the  loth  magnitude  or  smaller  (and  there  are  such), 
never  have  tails,  whilst,  on  the  other  hand,  such  a  thing  as  a 
large  and  compact  comet  visible  to  the  naked  eye  and  without 
a  tail  is  unknown.  It  is  true  that  one  or  two  comets  are  on 
record  as  tailless,  and  as  large  in  size  as  a  Full  Moon,  but  our 
knowledge  of  them  depends  upon  ancient  writers  whose 
habitual  looseness  of  language  and  lack  of  precision  seriously 
discount  their  testimony. 

It  will  now  be  desirable  to  describe  in  some  detail  certain  of 
the  features  which  have  been  recorded  in  the  case  of  comets 
seen  in  the  past.  In  the  first  place,  when  a  comet  has  a  tail, 
the  tail  is  nearly  always  turned  more  or  less  directly  away  from 
the  Sun  ;  that  is  to  say,  it  has  shot  forth  in  a  direction  behind 
the  comet  rather  than  in  front  of  it  or  towards  the  Sun.  This 
is  no  more  than  the  common  case  of  the  tail  of  anything, 
whether  it  be  the  train  of  a  queen  or  the  tail  of  a  cow. 
There  are  a  few  instances  on  record  of  comets  having  had 
not  only  a  normal  tail,  properly  so  called,  but  a  short  stubby 
tail  on  the  side  of  the  Sun  and  pointing  towards  the  Sun. 
Such  a  tail  is  usually  spoken  of  by  old  writers  as  a  "beard," 
and  the  sense  of  the  expression  will  be  obvious  from  what 
has  just  been  said  as  regards  tails  generally.  This  fact  of 
tails  of  comets  being  usually  turned  away  from  the  Sun  was 
noted  by  an  observant  foreigner  named  Apian  in  1531  ;  but 


152  COMETS. 

the  Chinese  seem  to  have  noticed  the  same  fact  700  years 
previously. 

When  a  comet  has  a  tail,  in  the  majority  of  cases  there  is 
only  one  such  appendage,  but  two  tails  are  not  uncommon,  and 
there  have  been  cases  of  three,  four,  and  five  tails,  whilst  the 
celebrated  comet  of  1744  had  six  well-defined  separate  tails. 
It  is  important  to  note  that  it  sometimes  happens  that,  though  a 
comet  can  only  be  fairly  described  as  having  one  tail,  yet  now 
and  again  there  may  be  noticed  long,  thin,  streaks  of  cometary 
matter  emanating  from  the  same  centre  as  the  main  tail,  and 
these  streaks  ought  rightly  to  be  numbered  as  distinct  tails. 
This  attribute  of  subsidiary  streamers  in  the  nature  of  tails 
was  not  in  the  past  very  much  dwelt  upon  by  observers 
describing  comets  which  they  had  studied  ;  but  the  application 
of  photography  to  cometary  observations  has  in  recent  years  in 
several  cases  brought  very  distinctly  under  our  notice  what 
must  really  be  spoken  of  as  a  multiplicity  of  tails.  Photo- 
graphy grasps  undoubtedly  a  wider  range  of  details  than  does 
human  vision  at  the  eye-end  of  a  telescope. 

Under  ordinary  circumstances,  while  a  common  type  of 
comet  has  a  common  type  of  simple  tail,  there  is  nothing  in 
general  to  catch  the  eye  and  lead  one  to  any  precise  conception 
of  the  actual  form  of  the  tail  ;  but  in  what  may  be  called 
more  perfectly  developed  tails,  one  sees  the  two  edges  dis- 
tinctly brighter  than  the  centre,  and  this  compels  the  conclusion 
that  the  real  form  of  such  a  tail  is  cylindrical,  or,  in  many  cases, 
conical.  That  a  tail  is  of  this  formation  is  obviously  suggested 
by  the  fact  that,  if  we  look  at  any  luminous  cylinder  sideways, 
even  if  really  illuminated  evenly  all  round,  it  will  in  projection 
look  brighter  at  its  apparent  edges,  because  the  eye  will  be 
viewing  the  edges  through  a  concentrated  thickness  of  material, 
whereas  the  portion  of  the  cylinder  midway  between  the 
illuminated  edges  will  only  be  of  a  single  thickness,  so  to 
speak.  This  may  be  tested  in  several  obvious  ways  in 
connection  with  domestic  illumination  in  our  houses,  and 


CLASSIFICATION    OF    TAILS. 


153 


assuredly  gives  us  a  clue  to  the  true  form  of  many  cometary 
tails. 

Where  a  comet  has  evidently  two  distinct  tails  (not  the 
appearance  of  two  tails  in  virtue  of  the  explanation  just  given) 
it  almost  always  happens  that  the  two  tails  are  of  different 
length,  and  that  the  shorter  one  is  inferior  in  brilliancy  to  the 
longer  one. 

Except  in  the  case  of  small  comets  with  short  tails,  it  is 
seldom  that  a  tail  is  straight ;  it  is  most  usual  for  the  tail  to 


Fig.  172.— Medal  distributed  by  the  Monks  to  avert  Misfortune 
during  the  Appearance  of  the  Great  Comet  of  1680. 

be  curved,  and  the  curvature  is  the  natural  result  of  the  comet's 
head  moving  forwards,  and  the  tail  not  being  able  to  keep 
pace  with  it  because  of  its  more  flimsy  material.  This,  at  least, 
seems  a  fair  and  proper  way  of  describing  the  condition  of 
things. 

Two  astronomers  of  the  present  day,  working  on  different 
lines,  have  endeavoured  to  classify  the  tails  of  comets  on  the 
supposition  that  there  is  an  individuality  about  tails,  which 
shows  that  they  are  not  all  formed  in  the  same  way  or  under 
similar  conditions.  The  most  svstematic  of  these  classifications 


154  COMETS. 

is  due  to  the  Russian  astronomer  Bredichin,  who  has  worked 
at  the  matter  with  great  zeal  and  moderation  and  discretion 
of  language  and  conclusions.  I  lay  stress  on  this  description 
of  his  labours  because  there  has  been  of  late  years  a  great 
disposition  on  the  part  of  astronomers  of  a  certain  sort  to  put 
forth  wild  speculations  respecting  the  formation  and  condition 
of  the  tails  of  comets,  with  a  very  limited  amount  of  proof 
available  to  support  their  views.  Bredichin's  investigations 
led  him  to  divide  the  tails  of  comets  into  three  classes:  (i) 
long,  straight  tails ;  (2)  curved,  plume-like  tails  ;  (3)  short, 
stubby,  and  sharply  curved  brushes  of  light. 

Bredichin's  First  Type  of  tails  he  considers  formed  of  matter 
upon  which  the  Sun  exercises  a  repulsive  action  very  much 
greater  than  the  Sun's  attractive  action  in  virtue  of  the  general 
principles  of  Gravitation,  so  that  the  particles  of  cometary 
matter  quit  their  point  of  origin  in  the  head  of  the  comet  with 
a  relative  velocity  which  rapidly  increases,  and  eventually 
becomes  enormous.  The  long,  straight  streamers,  which  I 
have  already  alluded  to,  were  well  exemplified  in  Bond's  draw- 
ings of  Donati's  comet  of  1858,  and  tails  of  this  type  are 
composed,  according  to  Bredichin,  of  hydrogen  gas.  The 
Second  Type  of  tail  is  by  far  the  most  usual  one.  Here  the 
repulsive  force  is  much  less  than  in  the  previous  case,  and 
the  comet  may  be  said  to  be  more  completely  and  continuously 
under  the  attractive  control  of  the  Sun.  Some  kind  of  hydro- 
carbon gas  is  suggested  as  the  constituent  of  tails  of  this  class. 
Tails  of  the  Third  Type,  because  they  do  not  seem  as  a  rule 
capable  of  much  expansion  of  size,  are  thought  not  to  be  subject 
to  any  great  amount  of  repulsive  influence,  but  to  be  dominated 
far  more  definitely  by  the  normal  laws  of  Gravitation.  The 
matter  of  which  they  are  composed  is  thought  to  be  in  a  state 
indicative  of  far  greater  heaviness  than  obtains  in  either  of 
the  two  previous  classes,  and  to  consist  of  the  vapour  of  iron, 
perhaps  also  of  sodium,  and  of  other  substances.  It  is  quite 
evident  that  these  points  are  of  a  very  speculative  character ; 


FIG.  173 


PLATE   LI 


154] 


Halley's  Comet,  Naked-eye  View  in  Mexico  (Z..  G.  Leon), 


FIG.  174 


PLATE    LI  I. 


Curious  Aspect  of  the  Head  of  Halley's  Comet,  June  8,  1910. 

(L.   G.  Leon.} 


L'55 


CLASSIFICATION    OF    TAILS.  155 

but  still  Bredichin's  ideas  cannot  be  condemned  as  destitute 
of  possibility  and  probability. 

An  experienced  American  astronomer,  Professor  W.  H. 
Pickering,  of  Harvard  College  Observatory,  divides  the  tails 
of  comets  into  two  classes,  and  sets  up  a  distinction  on  lines 
entirely  different  from  those  of  Bredichin.  He  seems  to  con- 
sider that,  either  simultaneously  or  successively,  as  the  case 
may  be,  a  tail  which  we  should  at  the  first  glance  regard  as  a 
simple  tail,  really,  when  carefully  looked  into,  may  comprise 
either  simultaneously  or  successively  a  tail  which  has  its  origin 
in  the  comet's  head,  surrounding  and  enveloping  which  there 
is  another  tail  (which  perhaps  rather  should  be  called  an  en- 
velope), which  is  of  a  different  and  uncertain  origin.  Pickering 
says  that,  "judged  by  the  photographs  of  recent  comets,  the 
former  kind  is  much  the  more  common  of  the  two,  and 
consists  usually  of  a  bunch  of  rays,  more  or  less  straight,  pro- 
ceeding from  the  nucleus  directly  away  from  the  Sun."  He 
thinks  that  his  second  type  of  tail  is  well  represented  in  the 
pictures  in  existence  of  the  "great  comet  of  1811,"  of  the 
"  great  comet  of  1901,"  and  of  the  first  comet  of  1910.  He 
considers  that  Swift's  comet,  of  1892  (i),  was  an  instance  of 
both  types  of  tail  being  present  at  the  same  time,  and  that 
Halley's  comet  in  1910  was  a  case  of  a  comet  having  a  tail 
of  a  different  type  after  its  perihelion  passage  from  what  it  had 
before  the  perihelion  passage  ;  that  at  the  earlier  period  the 
tail  had  its  origin  in  the  nucleus,  but  that  at  the  later  period 
the  tail  was  altogether  different,  and  was  a  large  envelope, 
wrapping  up  the  head,  but  distinct  from  it.  Pickering  goes 
on  to  suggest  that  the  enveloping  type  of  tail  is  much  smoother 
in  structure  than  the  type  which  issues  from  the  nucleus,  and 
that  it  is  the  kind  which  seems  to  have  been  present  in  at  least 
three  of  the  five  great  comets  of  the  igth  century,  namely, 
thoseofiSii,  1858,  and  1882. 

The  foregoing  classifications,  however  we  may  regard  them, 
do  not  directly  help  us  in  coming  to  a  conclusion  as  to  the 


156  COMETS. 

originating  cause  of  a  tail  where  a  comet,  when  discovered,  is 
tailless,  and  afterwards  becomes  furnished  with  a  tail.  As  to 
this  the  theory  generally  favoured  by  astronomers  nowadays 
is  that  what  is  called  "  light  pressure "  is  concerned  in  the 
creation  of  cometary  tails,  probably  under  impulses  which 
cannot  yet  be  defined  or  explained,  but  which  are  of  electrical 
character.  "  Light  pressure,"  as  a  phrase  standing  by  itself, 
may  conveniently  be  defined  as  being  based  on  the  supposition 
that  all  sources  of  light  exercise  a  sort  of  repulsive  push  on  all 
materials  on  which  the  light  impinges,  whatever  may  be  the 
source  of  the  light  or  the  nature  of  the  material. 

Thus  far  the  attention  of  the  reader  has  only  been  called 
to  a  few  general  propositions  which  might  throw  light  upon 
naked-eye  observations  of  any  casual  comet  which  might 
appear ;  but  much  more  must  be  said  if  we  would  obtain  a 
comprehensive  grasp  of  cometary  astronomy.  The  question 
of  the  number  of  the  comets  and  of  their  paths  through  space 
opens  up  a  variety  of  topics  which,  though  in  a  certain  sense 
subsidiary  to  what  has  gone  before,  are  of  the  greatest  intrinsic 
interest. 

In  olden  times  it  was  not  considered  that  comets,  as  regards 
their  movements,  were  subject  to  any  laws,  but  that  they  came 
and  went  away  in  a  perfectly  haphazard  fashion.  It  was  not 
until  quite  modern  times  that  it  was  realised  that  they  were 
subject,  to  a  certain  extent,  to  the  same  laws  of  motion  as 
operated  in  the  case  of  the  planets.  The  situation  of  things 
is  this  :  whilst  it  is  true  that  a  large  number  of  comets  come 
to  us  from  whence  we  know  not,  and  then  pass  away  whither 
we  know  not,  yet  there  are  a  certain,  not  inconsiderable, 
number  which  may  be  regarded  as  permanent  members  of 
the  solar  system,  and  come  and  go,  and  after  a  certain  interval 
come  back  again.  These  are  termed  "  periodical  comets," 
and  bear  a  certain  analogy  to  the  planets  as  regards  their 
movements,  the  principal  point  of  difference  being  that,  whereas 
the  planets  all  move  in  orbits  not  materially  differing  from 


FIG.  175 


PLATE   LIII. 


The  Great  Comet  of  1811, 


FIG.  176 


PLATE   LIV. 


JS 


[157 


PERIODICAL   COMETS.  157 

circles,  not  a  single  comet  moves  in  an  orbit  which  is  anything 
like  a  circle.  The  orbits  of  the  periodical  comets  are  all  of 
them  ellipses  of  great  eccentricity.  Perhaps  this  will  be  better 
understood  by  saying  that  all  the  periodical  comets  move  in 
oval  orbits,  which  may  be  compared  roughly  to  flattened  circles. 

The  orbits  of  the  periodical  comets  not  only  differ  much  in 
eccentricity,  but  also  in  their  dimensions.  Thus  it  comes 
about  that  Encke's  comet,  with  its  period  of  only  a  little  more 
than  three  years,  performs  its  journey  round  the  Sun  in  an  orbit 
within  that  of  the  planet  Jupiter,  whilst  Halley's  comet  travels 
so  far  away  from  the  Sun  in  the  course  of  its  voyage  of  75 
years  that  when  at  its  greatest  distance  it  is  quite  outside 
what  we  call  the  solar  system,  because  it  attains  a  point 
outside  the  orbit  of  Neptune,  the  most  remote  of  the  known 
planets. 

The  comets  which  are  not  periodic  so  far  as  we  know,  come 
to  us  in  paths  which  the  mathematician  calls  "parabolas"  and 
"  hyperbolas,"  though  the  number  of  the  comets  which  have 
been  known  for  a  certainty  to  have  pursued  hyperbolic  orbits 
are  very  limited. 

Going  back  to  the  periodic  comets— whilst  the  known  or 
supposed  periods  vary  between  a  handful  of  years  and  thou- 
sands of  years,  they  may  be  roughly  grouped  in  three  classes  : 

(1)  Comets  with  periods  between  3  and  15  years. 

(2)  Comets  with  periods  averaging  70  years. 

(3)  Comets  with  periods  of  many  hundreds  of  years. 

Of  only  those  comets  which  belong  to  Classes  I  and  2  can  it 
be  positively  asserted  that  they  are  permanent  members  of  the 
solar  system.  This  is  certain,  because  they  have  proved  their 
allegiance  to  the  Sun  by  having  paid  him  more  than  one  visit ; 
indeed  several  of  them  have  paid  several  visits.  Our  know- 
ledge of  the  comets  in  the  third  class  is  much  less  certain,  for 
the  reason  that,  owing  to  the  length  of  their  periods,  no  oppor- 
tunity has  yet  occurred  for  them  to  pay  us  a  return  visit.  There 
is  indeed  one  comet  of  long  period  which  astronomers  once 


158 


COMETS. 


hoped  might  safely  be  regarded  as  a  permanent  member  of  the 
system ;  but  the  supposition  still  lacks  proof.  There  appeared 
in  1556  a  brilliant  comet  which  was  thought  at  one  time  to  be 
a  second  appearance  of  the  great  comet  of  1264,  one  of  the 
grandest  on  record.  Its  return  about  1860  was  confidently 
reckoned  on  by  many  astronomers,  but  all  were  disappointed. 
There  have  been  other  comets  observed  during  recent  years, 
which,  it  has  been  calculated,  move  in  elliptic  orbits,  and  must 
therefore  be  periodic  in  a  literal  sense ;  but,  as  the  periods  of 
some  of  these  amount  to  thousands  of  years,  it  is  evident,  not 
only  that  the  world  will  have  to  wait  for  a  very  long  time  before 
seeing  them,  but  also  that  doubt  attaches  to  the  exact 
characters  of  their  orbits,  owing  to  the  vast  extent  of  the 
same,  to  say  nothing,  in  some  instances,  of  the  lack  of  a 
sufficient  number  of  trustworthy  observations  when  they  were 
within  our  reach. 

The  following  are  the  names  of  the  short-period  comets 
which  may  be  regarded  as  well-recognised  members  of  the 
solar  system  : — 


No. 

Name. 

Period 
in  years. 

Next 
retui  n. 

I. 
2. 

3- 

4- 
5 

Encke's         .         .         .                 ; 
Tempel's  Second  (1873,  ii.)  . 
Tempel-Swift's      .         .         . 
Winnecke's    .         .         .       •".         ;  • 

3-29 

5!S 

5'53 
5'54 
5-58 

1914 
1914 
1914 

*9*5 

1912 

6. 

7 

Finlay's         ..... 
D'Arrest's      

6-54 
664 

1913 
1917 

8. 

Wolfs   

676 
685 

1918 
i9T3 

10. 
n. 

I  2 

Borelly's        
Brooks's  Second  (1889  v.)      . 

7-00 
707 

7'44 

1918 
1917 
1918 

13 

Tuttle's  

13-66 

19*3 

FIG.  177 


PLATE    LV. 


15.31 


FIGS.   178-183 


PLATE  LVI. 


June  30. 


July  6. 
Thft   nntnp.t  nf  18fiO. 


July 
(  r.a.-b<hp.Up.tt.i   and 


FAMILIES  OF  COMETS. 


159 


With  reference   to  two  or  three  of  the  comets  in  the  fore- 
going list,  the   date  of  whose  next  return   is  suggested,  it   is 


Fig.  184.— The  Comet  Families  of  Saturn,  Uranus,  and  Neptune 

(Drawn  by   H.   C.  Wilson). 

to  be  understood  that,  though  they  have  made  several  returns 
in  the  past,  they  have  not  been  seen  very  recently,  and  in  some 
degree  a  mystery  hangs  over  them,  their  orbits  appearing  to 


i6o 


COMETS, 


have  been  deranged  by  the  influence  of  the  planet  Jupiter. 
The  whole  group  of  13  consists  of  small  comets  not  as  a  rule 
visible  to  the  naked  eye,  though  some  of  them  are  some- 
times so  visible  when  favourably  placed  with  respect  to  the 
Earth  and  the  Sun. 

All  the  comets  in  the  list  on  p.  158,  except  Tuttle's,  are  to 
be  regarded  as  members  of  what  is  called  the  "  Jupiter  family 
of  comets,"  and  some  other  comets  whose  orbits  are  not  at 
present  well  established  will  probably  be  put  in  the  same  group 
at  a  future  time.  It  is  considered  now  that  all  the  superior 
planets  beyond  Jupiter,  namely,  Saturn,  Uranus,  and  Neptune, 
have  "  families  "  of  comets  associated  with  them. 

The  long-period  comets  which  are  recognised  as  being 
those  which  it  is  safe  to  regard  as  members  of  the  solar 
system,  though  not  all  of  them  have  been  seen  twice,  are  the 
following : — 


No. 

Name. 

Period 
in  years. 

Next 
return. 

I. 
2. 

Westphal's(i852,  iv.)    . 
Pons's(i8i2)         .... 

6o(?) 
70-68 

1913 

J955 

3- 

Di  Vice's  (1846,  iv.)      . 

73'25 

1919 

4- 

Olbers's  (1815)      .... 

74'5 

iq6o 

5- 

Brorsen's  (1847,  v.) 

74'97 

1922 

6. 

Halley's        

76-78 

1986 

The  only  one  of  these  six  comets  which  calls  for  any  special 
mention  is  the  last-named,  Halley's ;  but  the  story  of  Halley's 
comet  is  now  so  well  known  that  it  would  be  tedious  to  give  it 
at  any  length. 

Sir  Isaac  Newton  and  Edmund  Halley  share  between  them 
the  honours  of  the  comet  which  now  bears  the  name  of  the 
latter,  and  even  in  a  skeleton  form  its  story  is  very  interesting. 
Sir  Isaac  Newton  gave  to  the  world  in  1687  his  celebrated 


HALLEY'S  COMET.  161 

treatise  on  Universal  Gravitation  which  is  best  known  by  the 
simple  name  Principle  but  of  which  the  full  title  is  Philoso- 
phice  Naturalis  Prinoipia  Mathematica.  The  cost  of  publishing 
this  book  appears  to  have  been  borne  by  H alley,  and,  after 
studying  his  venture,  the  idea  came  into  his  head  to  try  and 
see  whether  Newton's  labours  could  be  utilised  for  obtaining 
some  insight  into  the  movements  of  comets.  A  comet  seen 
by  Halley  himself  in  1682,  though  not  discovered  by  him, 
seemed  to  offer  the  desired  opportunity,  and  he  calculated  its 
orbit  on  Newton's  principles.  One  thing  led  to  another,  and, 
after  finishing  his  calculations  with  regard  to  the  comet  of 
1682,  he  turned  his  attention  to  the  recorded  observations  of 
comets  which  had  appeared  in  1607  and  1531.  The  results 
as  to  the  nature  of  their  orbits  were  so  nearly  identical  in 
all  particulars  that  he  did  not  long  hesitate  in  coming  to  the 
conclusion  that  the  three  comets  were  really  one  comet,  and 
that  therefore  it  was  a  periodical  member  of  the  solar  system. 
He  had  sufficient  confidence  in  his  own  work  to  venture  on  the 
prediction  that  the  comet  would  return  again  about  1758  ;  and 
so  it  did.  The  story  of  its  discovery  on  the  night  of  Christmas 
Day  of  that  year  by  a  Saxon  farmer  named  Palitzsch,  living  near 
Dresden,  and  of  the  calculations  made  in  anticipation  of  its 
return,  is  a  thrice-told  tale.  Halley  died  in  1742,  and  left 
behind  him  a  plaintive  record  of  his  hopes  that  "  impartial 
posterity  will  not  refuse  to  acknowledge  that  this  [periodicity] 
was  first  discovered  by  an  Englishman." 

Halley's  Comet  paid  another  visit  to  these  parts  of  Space  in 
1835,  and  the  whole  subject  of  mathematics  as  applied  to  orbits 
had  made  such  progress  between  1758  and  1835  that  the  comet's 
perihelion  passage,  as  calculated,  was  found  to  be  wrong  only 
to  the  extent  of  about  4  days. 

The  last  return  of  Halley's  Comet  to  perihelion  in  the  spring 
of  1910  will  be  fresh  in  the  minds  of  all  my  readers — how  it  was 
for  the  inhabitants  of  the  northern  hemisphere  a  great  disap- 
pointment, whilst  dwellers  on  the  opposite  side  of  the  world 
ii 


1 62  COMETS. 

enjoyed  a  magnificent  sight.  The  pictures  annexed  will  give 
its  appearance  at  various  times,  and  as  seen  in  various  places. 
In  England  it  showed  itself  as  quite  an  ordinary  comet,  just 
visible  to  the  naked  eye,  and  not  very  conveniently  placed, 
being  near  the  Sun  in  the  evening  twilight.  But,  after  its  peri- 
helion passage  on  April  19,  when  it  had  passed  round  to  the 
other  side  of  the  Sun,  and  was  visible  in  the  early  morning, 
those  who  had  that  opportunity  by  reason  of  their  being  in 
Africa,  Australia,  or  New  Zealand,  saw  the  comet  as  a  magnifi- 
cent object  with  a  tail  extending  half  over  the  celestial  vault. 

The  world-wide  interest  felt  in  Halley's  Comet  in  1910  is 
well  shown  by  the  following  account  of  it  which  came  from  the 
far-off  island  of  New  Guinea : 

"  On  May  9  the  comet,  looking  like  a  muffled  star,  was  seen 
in  the  East,  and  its  tail,  a  broad  beam  of  brilliant  light,  ex- 
tended upwards  through  about  30°.  Below  the  comet  and  a 
little  to  the  South  of  it  Venus  shone  like  a  little  moon,  appear- 
ing far  bigger  than  any  planet  I  have  ever  seen.  The  comet 
grew  enormously,  and  in  the  early  morning  of  May  14,  the  last 
time  that  we  saw  it  completely  before  it  had  passed  the  Earth,1 
.the  tail  blazed  across  the  heavens  like  an  immense  searchlight 
beam  to  the  zenith  and  beyond.  On  May  26  it  appeared 
again  in  the  evening  reduced  in  size  to  about  45°,  and  several 
nights  we  watched  it  growing  always  smaller,  until  it  vanished 
from  our  sight.  Superlative  expressions  will  not  describe 
Halley's  Comet  as  we  saw  it  in  New  Guinea  ;  it  was  a  wonder- 
ful appearance  and  one  never  to  be  forgotten.  Our  coolies 
and  the  Javanese  declared  that  it  portended  much  sickness 
and  death.  Though  we  tried  to  question  them  about  it,  we 
never  learnt  how  it  impressed  the  minds  of  the  natives."  2 

A  matter  which  caused  much  discussion,  both  as  a  matter  of 
prophecy  and  fulfilment  (or  non-fulfilment),  was  whether  the 
comet  had  crossed  the  Sun  as  seen  from  the  Earth,  and 
whether  it  had  been  detected  whilst  doing  so.  The  conclusions 

1  A  probable  mistake  for  Sun. 

3  WOLLASTON,  Pigmies  and  Papuans* 


FIG.  i8c; 


PLATE   LVII. 


Halley's  Comet,  May  1,  1910. 

Photographed  at  the  Transvaal  Observatory. 


FIGS.   186-191 


PLATE   LVIII. 


May  5,  3-l5-l-45  a.m.  C.T.S. 


May  13,  3.10-3.37  a.m.  C.T.S. 


May  30,  9.20-9.60  p.m.  C.T.S.  June  5,  10.00-10.30  p.m.  C.T.S. 

Halley's  Comet,  1910  (D.  W.  Morehouse). 

[163 


HALLEYS    COMET    IN    IQIO. 


1 63 


arrived  at  were  indeterminate  :  it  is  probable  that  the  comet  did 
cross  the  Sun's  disc,  and  ought  to  have  been  seen,  but  it  was 
not  seen.  On  the  other  hand,  it  appears  quite  certain  that  the 
Earth  passed  through  some  part  of  the  comet's  tail,  though 
nothing  inconvenient  happened. 

It  may  be  stated,  by  the  way,  that  the  question  of  a  collision 


JUNE  6 


SCOMKI 


EARTH 


Fig.  192.— Path  of  Halley's  Comet,  1910. 


between  a  comet  and  the  Earth  has  often  occupied  men's  minds 
in  past  times,  and  given  rise  to  panics  ;  but  there  never  has  been 
the  slightest  justification  for  alarm.  It  is  quite  certain  that  in 
1 86 1  the  Earth  passed  through  a  very  thick  part  of  the  tail  of 
the  great  comet  of  that  year,  but  nothing  happened  beyond  a 
sensation  of  fogginess  which  impaired  the  light  of  the  Sun, 


164 


COMETS. 


shining  at  the  time,  and  led  in  one  case,  at  least,  to  a  demand  for 
artificial  light  at  the  early  hour  of  7  p.m.  on  June  30,  when  it 
was  also  noted  that  the  sky  had  a  yellow  auroral  glare,  the  Sun 
shining,  but  not  as  usual. 

To  give  a  list  of  all  the  comets  to  which  might  be  applied  the 
adjective  "  celebrated,"  and  still  more  to  describe  them,  would 
run  into  many  pages.  Let  it  suffice,  then,  to  mention  the 
following,  belonging  to  the  igth  century:  1811,  1825,  1843, 
1858,  1861,  1874,  1880,  and  1882.  Thus  far  in  the  2Oth  century 
we  have  had  only  Halley's  (1910),  and  one  or  two  which  can 

only  be 
described 
as  good 
second- 
class 
c  o  m  e  t  s 
(1902,  i.  ; 
1910,  i.). 

The 
spectro- 
scope has, 
of  course, 
been  ap- 
plied to 

comets,  as  to  other  celestial  objects.  The  general  result  is 
to  show  that  cometary  spectra,  more  often  than  not,  belong 
to  one  type  only,  that  of  the  hydro-carbons. 

Up  to  the  present  time  historians  and  astronomers  together 
have  recorded  a  total  of  about  uoo  comets.  Of  course  down 
to  the  1 7th  century  the  comets  noted  were  all  naked-eye 
ones  ;  but,  seeing  how  nowadays  the  naked- eye  comets  fall 
short  in  number  of  the  telescopic  comets,  it  is  safe  to  assert 
that,  since  the  Christian  era,  several  thousand  cornets  have 
visited  our  system. 

In  case  a  reader  may  be  surprised  at  the  number  of  comets 


Fig.  193.— The  Warner  Prize  Medal. 


165 


1 66  COMETS. 

discovered  in  America  of  late  years  having  been  so  large  com- 
pared with  the  number  discovered  in  all  other  parts  of  the  world, 
it  may  be  worth  while  to  mention  that  in  America  prizes  in 
money  and  medals  are  systematically  awarded  to  those  who  are 
able  to  prove  priority  in  picking  up  new  comets.  The  Warner 
gold  medal,  illustrated  on  p.  164,  is  one  of  the  stimulants  which 
American  astronomers  have  before  them  to  encourage  zealous 
work  on  behalf  of  science. 

This  chapter  may  be  usefully  concluded  by  some  brief  notes 
in  detail  on  the  comets  which  have  been  selected  to  illustrate  it. 


THE  GREAT  COMET  OF  1744. 

This  comet  historically  was  long  a  mystery,  for  the  statement 
that  it  had  6  tails,  announced  in  books  all  over  the  world,  was 
very  generally  distrusted  because  it  depended  on  the  unsup- 
ported testimony  of  one  man.  But  some  years  ago,  in  a  curious 
way,  there  came  out  evidence  of  a  contemporary  writer  that  the 
comet  had  really  possessed  a  number  of  separate  tails  ;  and  the 
illustration  here  given  shows  that  there  were  not  only  six,  but 
considerably  more  than  six  tails.  The  number  of  six  seems  to 
have  been  arrived  at  by  counting  the  streamers  in  pairs,  each 
pair  comprising  the  two  sides  of  one  tail  properly  so-called. 


THE  GREAT  COMET  OF  1843  (i.). 

This  comet  appeared  with  great  suddenness,  and  was  endued 
with  peculiarly  rapid  motion,  and  had  a  tail  fully  100°  long.  It 
would  seem  to  have  been  one  of  the  grandest  comets  on  record, 
and,  comparing  together  the  testimony  of  those  who  on  the  one 
hand  had  seen  the  great  comet  of  1811  as  well,  and  on  the 
other  hand  those  who  had  not  seen  1811  but  had  seen  Donati's 
Comet  of  1858,  I  consider  that  one  is  justified  in  saying  that 
the  1843  comet  was  the  grandest  of  the  iQth  century  in  point  of 
size  and  brilliancy. 


FIG.   195 


PLATE    LIX. 


Coggia's  Comet,  1874,  on  July  13  (F.   Brodie). 


1661 


FIG.  196 


PLATE   LX. 


[i66« 


FIGS.  197-198 


PLATE    LXI. 


FIGS.    199  200 


PLATE    LX1I. 


Nov.  13. 


and 


Nov.  21. 
nf  thp 


Tftrnpt    of    1882. 


FIGS.  201-202 


PLATE   LXIII. 


FIGS.  203-204 


PLATE   LXIV. 


[167 


CELEBRATED    COMETS.  167 


DONATI'S  COMET,  1858  (vi.). 

This  comet,  though  inferior  in  size,  as  just  stated,  to  the  great 
comet  of  1843,  may  be  regarded  as  having  been  the  most 
beautiful  comet  of  the  igth  century,  owing  to  its  plume-like 
shape,  and  to  its  possession  of  certain  long,  straight  streamers 
not  reproduced  in  the  engraving.  The  star  visible  near  the 
comet's  head  is  Arcturus. 


THE  COMET  OF  1860  (Hi.). 

This  comet  was  not  one  of  very  remarkable  size,  but  the 
pictures  are  given  for  the  reason  that  they  exemplify  in  a  strik- 
ing degree  the  jet-shaped  emanations  which  occasionally  are 
noticed  to  proceed  from  the  head  of  a  comet.  This  feature  was 
also  brought  out  in  a  very  marked  manner  in  the  comet  of 
1862  (ii.). 

COGGIA'S  COMET,  1874  (iv.). 

Coggia's  Comet  of  1874  may  be  described  as  a  good  specimen 
of  a  second-class  fine  comet.  It  was  a  striking  object  in  the 
evening  sky  during  the  month  of  July,  but  it  is  engraved  in  this 
book  as  being  a  good  example  of  the  way  in  which  some  comets 
seem  to  shed  off  independent  envelopes,  or  shells  of  matter,  one 
after  another. 

THE  GREAT  COMET  OF  1882  (iii.). 

This  was  a  fine  naked-eye  comet,  with  a  tail  very  much  in  the 
shape  of  a  Turkish  scimitar.  The  main  tail  gave  one  the 
impression  of  being  inside  a  long  and  wide,  but  very  ethereal  or 
flimsy,  envelope.  But  the  special  feature  of  this  comet  was  its 
nucleus,  which  was  and  still  is  unique  in  its  form.  It  was 
elliptical,  and  of  great  length  in  proportion  to  its  breadth  ;  it 


1 68  COMETS. 

was  placed  longitudinally  with  regard  to  the  general  direction 
of  the  tail  ;  and,  to  crown  all,  instead  of  having  the  usual  one 
special  bright  centre,  it  was  always  seen  to  have  three  bright 
centres,  sometimes  four,  and  on  one  occasion  a  fifth  was 
suspected,  all  of  them  a  little  distance  from  one  another. 

SWIFT'S  COMET,  1892  (i.). 

We  have  passed  now  from  the  epoch  of  hand-drawn  pictures 
of  comets  to  representations  based  upon  photography.  Whilst 
it  is,  of  course,  a  truism  that  the  Sun  is  a  more  accurate  drafts- 
man than  the  human  eye  and  hand  together,  it  must  be  confessed 
that  photography  often  fails  to  bring  home  to  the  eye  many 
details  which  sometimes  strike  even  the  most  inattentive 
observer. 

But  this  cuts  both  ways,  because  not  only  in  the  case  of 
comets,  but  also  in  the  case  of  nebulae,  photography  frequently 
catches  features  which  are  invisible,  not  only  in  the  telescope 
used  by  a  particular  observer,  but  in  all  telescopes,  whatever  may 
be  their  size.  It  was  owing  to  photography  that  Swift's  Comet 
was  the  first  to  bring  out  features  connected  with  the  tails  of 
comets  which  may  be  said  to  have  revolutionised  our  ideas  as 
to  the  physical  condition  of  those  bodies.  Barnard  well  remarks 
that  this  "  has  occurred  in  the  case  of  comets  with  which  the 
older  method  of  observing  would  have  promised  little  or  nothing 
of  interest."  Swift's  comet  may  be  mentioned  as  one  of  those 
which  seemed  to  be  endued  with  a  rotation  of  the  head  and  tail 
about  an  axis  passing  lengthwise  through  the  tail. 

RORDAME'S  COMET,  1893  (ii.), 

illustrates  a  remark  in  the  last  paragraph  about  photography, 
bringing  out  details  not  readily  grasped  by  the  naked  eye,  for 
some  of  its  peculiarities  are  of  the  same  sort  as  those  of  Swift's 
Comet. 


FIGS.  205-208 


PLATE    LXV. 


J68] 


FlGS.    20Q-2I2 


PLATE   LXVI. 


.I68« 


FIGS.  213-214 


PLATE    LXVIT. 


I68&] 


FIGS.  21  s-2i6 


PLATE    LXVIII. 


Oct.    21. 


Oct.  22. 

Brooks's  Comet  of  1893  (iv.). 


(168 


FIG.   217 


PLATE   LXIX. 


Borelly's  Comet  of  1903  (iv.),  ( /?.  /.  Wallace}. 


I68./J 


FIG.  218 


PLATE    LXX. 


Dec.  29,  1905. 
Giacobini's  Comet  of  1906  (i.),  (E.  E.  Barnard}. 


FIGS.  219-220 


PLATE  LXXI. 


Dec.  29,  1905. 


168  f] 


Jan.  5,  1906. 

Giacobini's  Comet  of  1906  (i.),  (E.  E.  Barnard}. 


FIG.  221 


PLATE   LXXII. 


REMARKABLE   COMETS.  169 

BROOKS'S  COMET  OF  1893  (iv.). 

This  seems  to  have  been  a  comet  damaged  by  some  external 
violence,  strange  as  the  idea  may  seem.  Barnard  wrote  thus 
about  it  : — 

"  Indeed,  the  singular  freaks  of  that  comet's  tail  compel  us 
to  seek  an  explanation  in  some  outside  cause — inherent  neither 
in  the  comet  nor  in  the  Sun.  The  tail,  which  one  day  was  in 
a  normal  condition,  was  on  the  next  broken  and  disturbed,  as 
if  it  had  encountered  some  resisting  medium  in  its  flight 
through  space.  The  disturbance  seemed  to  come  from  the 
direction  towards  which  the  comet  was  moving.  On  the  suc- 
ceeding morning  it  was  badly  broken,  and  hung  in  cloud-like 
masses,  some  of  which  were  entirely  torn  off  from  the  tail  and 
appeared  to  be  drifting  away  in  space.  On  another  occasion 
the  tail  was  concave  towards  the  direction  of  motion,  and  had 
the  appearance  of  beating  against  a  current  of  resistance.  It 
was  disjointed  in  places,  and  near  the  end  was  abruptly  bent 
at  nearly  a  right  angle,  as  if  at  that  point  it  had  encountered  a 
stronger  current  of  resistance.  If  one  examines  these  pictures 
there  seems  no  escape  from  the  conclusion  that  this  comet's 
tail  did  actually  encounter  some  resisting  or  disturbing  medium 
about  October  21,  1893,  and  for  several  days  subsequent  to  that 
date  ;  whether  this  was  a  swarm  of  meteors — such  as  we  know 
exist  in  space  near  the  Sun,  or  some  sort  of  resisting  matter,  of 
which  we  as  yet  know  nothing,  is  a  subject  for  time  to  settle." 

BORELLY'S  COMET,  1903  (iv.). 

This  comet  manifested  signs  of  disintegration  of  a  curious 
nature— that  is  to  say,  signs  of  a  part  of  its  tail  having  actually 
broken  off  from  the  main  tail ;  which  latter,  after  losing  the 
aforesaid  fragment,  began  to  grow  again  in  consequence  of  a 
new  supply  of  matter  being  forthcoming  from  the  nucleus. 

GIACOBINI'S  COMET,  1906  (i.). 

Observations  of  this  comet  were  unfortunately  much  interfered 
with  owing  to  the  prevalence  of  bad  weather  ;  but,  notwith- 


170  COMETS. 

standing  this,  Barnard  got  some  good  photographs  of  it,  and 
was  also  able  to  make  some  striking  notes.  He  says  that  the 
comet's  appearance  on  December  29,  1905,  was — 

"in  some  respects  quite  unique.  From  a  rather  large  head 
and  a  slender  neck,  the  tail  widens  out  on  each  side  in  a 
graceful  curve,  which  partly  closes  in  again  and  gives  a  strong 
convexity  to  the  tail.  The  edges  of  these  convexities  are 
sharply  defined,  and  are  outlined  by  a  rather  narrow  bright  rim 
or  border.  The  appearance  of  the  tail  strongly  suggests  a 
hollow,  convex,  transparent  cone  with  a  sensible  thickness.  A 
straight-edge  placed  along  the  sides  of  the  tail  shows  this 
convexity  strikingly,  as  may  be  seen  on  an  examination  of  the 
plate.  I  have  not  noticed  quite  this  appearance  before  in  a 
comet's  tail." 

DANIEL'S  COMET,  1907  (iv.). 

The  original  negative  of  this  comet  showed  the  tail  to  have 
six  branches,  but,  owing  to  the  extreme  faintness  of  two  of 
them,  only  four  are  depicted  in  the  illustration.  The  star  near 
the  end  of  the  tail  with  a  black  dot  in  it  was  y  Geminorum. 

MOREHOUSE'S  COMET,  1908  (Hi.). 

This  comet,  though  not  in  itself  a  very  large  one,  attracted 
considerable  notice  in  the  astronomical  world  owing  to  the 
transformations  which  it  underwent.  The  two  pictures,  both 
dated  October  1 5,  taken,  one  in  England  and  the  other  in 
America,  within  a  few  hours  of  one  another,  will  give  a  clue  to 
the  cause  of  this  excitement.  Barnard's  photograph  vividly 
brings  out  the  fact  that  the  tail  of  the  comet  underwent  a 
serious  and  real  disruption. 

H ALLEY'S  COMET,  1910  (ii.). 

So  much  has  been  said  already  about  Halley's  Comet  that 
it  seems  only  necessary  here  to  remind  the  reader  that  it  was 
only  in  the  Southern  Hemisphere,  and  after  the  comet  had 


FIG.  222 


PLATE   LXXIII. 


On  Oct.  15,  at  14  h.  3iTm. 

Morehouse's  Comet  of  1908  (Hi.),  (E.   E.   Barnard}. 


170] 


FIGS.  223-224 


PLATE   LXXIV. 


Nov.  15,  12  h.  6  m.  G.M.T. 

Morehouse's  Comet  of  1908  (iii.),  (Yerkes  Observatory).  [170* 


FIG.  225 


PLATE    LXXV. 


Morehouse's   Comfit  of  1908  (iii.\.  on   Nov.  13. 


FIGS.  226-229. 


PLATE  LXXVI. 


May  25. 


May  27. 


May  28.  June  2. 

Halley's  Comet,  1910  (C.  H.  Gingrich}. 


PLATE  LXXVII. 


The  Daylight  Comet  of  1911  (W.  B.  Gibbs}. 

As  seen  in  North  Africa. 


FIGS.  231-232 


PLATE   LXXVIII. 


o 

f 

o 


REMARKABLE    COMETS.  171 

passed  its  perihelion,  that  the  most  striking  views  of  it  were 
obtained.  Hence  it  comes  about  that  the  pictures  here  given 
may  excite  distrust  as  to  their  accuracy  on  the  part  of  dwellers 
in  the  Northern  Hemisphere. 

BROOKS'S  COMET,  1911  (<:). 

The  picture  dated  Sept.  24  [Plate  LXXVIII.]  brings  out 
the  case  of  a  comet  with  a  very  large  head  having  a  very 
slender  tail  proceeding  from  it.  The  photograph  vividly  recalls 
to  my  mind  one  of  the  earliest  comets  I  ever  saw.  I  am  not 
certain  of  the  exact  name  and  date,  though  I  think  it  was  one 
of  three  visible  in  the  summer  of  1857,  discovered  by  Klinkerfues 
at  Gottingen  on  August  20. 

By  way  of  a  last  word,  it  may  be  well  to  explain  why,  in 
nearly  all  cases,  the  stars  which  appear  in  the  comet-pictures 
given  in  this  volume  show  as  streaks  and  not  as  points.  It  is 
because  the  several  comets  being  themselves  in  motion,  it  is 
always  necessary,  when  long  exposures  are  desired  (in  order 
to  get  good  views  of  the  comets),  that  the  driving-clocks  of  the 
telescopes  employed  should  be  timed  to  keep  pace  with  the 
comets  rather  than  with  the  diurnal  movement  of  the  stars. 


CHAPTER   X. 
SHOOTING-STARS. 

Various  classes  of  luminous,  meteors. — Shooting-stars. — Fireballs. — 
Aerolites. — Radiant  points  of  shooting-stars. — Account  of  the  most 
important  showers. — Position  in  the  heavens  of  some  of  the  chief 
radiant  points. — Historical  allusions. — Celebrated  great  showers. 
— Fireballs. — Their  general  resemblance  to  one  another. — Re- 
markable fireballs  described  by  Webb  and  Brodie. — Their  sizes, 
distances,  and  movements. — Computation  of  their  paths. — Connection 
between  meteors  and  comets. — Shooting-stars,  fireballs,  and  aerolites 
all  of  the  same  nature. — Circumstances  attending  the  fall  of  aerolites. 

"  SHOOTING-STAR  "  is  the  popular  name  for  a  celestial  object 
which  is  scientifically  spoken  of  as  a  "  luminous  meteor,"  and 
luminous  meteors  are  subdivided  into  small  luminous  meteors 
and  fireballs,  with  what  are  called  aerolites  thrown  in. 
Though  the  first  two  subdivisions  are  visually  closely  allied, 
the  third  may  seem  to  be  somewhat  detached,  though  it  is  not 
so  in  reality.  A  simple  shooting-star  is  just  exactly  what  its 
name  imports  at  first  sight — a  star  which  shoots  ;  yet  it  is  not 
a  star,  and  it  does  not  shoot. 

Postponing  for  a  while  a  consideration  of  the  nature  of  all 
these  bodies,  we  will  first  of  all  consider  how  and  when  they 
show  themselves.  It  is  safe  to  say  that  several  shooting-stars 
may  be  seen  on  any  clear  night  throughout  the  year  when  the 
air  is  transparent  and  the  Moon  is  absent.  Thoughtlessly 
looked  at,  the  observer  will  fancy  that  they  dart  forth  casually 
in  the  sky,  first  at  one  point  and  then  at  another  point  ;  but 
such  is  not  the  case.  It  is  true  that  these  isolated  meteors 

172 


FIG.  233 


PLATE   LXXIX. 


A  Meteor  in  Flight  (E.  E.  Barnard). 

("The  object  gradually  increased  in  brilliancy,  and  as  gradually  faded 
172]  out,  ending  in  two  short  flashes  of  light.") 


FIG.  234 


PLATE  LXXX. 


^ 

i 

•3 
| 

o- 

w 


[173 


TELESCOPIC    METEORS. 


173 


used  to  be  thought  independent  of  one  another,  and  they  were 
formerly  called  "  sporadic  "  meteors,  which  meant  that  they 
were  haphazard  outbursts  of  light.  The  designation  has, 
however,  now  lost  nearly  all  its  importance  and  significance, 
because  the  prolonged  observation  which  has  been  given  to 
these  bodies  during  recent  years  has  enabled  astronomers  to 
realise  that  they 
belong  to 
families,  each 
with  its  own 
centre  in  the 
heavens,  which 
is  called  its 
"radiant  point." 
The  recognised 
radiant  points 
are  now  very 
numerous,  in- 
deed, several 
hundred  in 
number  ;  but  of 
these  the 
majority  would 
not  readily 
attract  notice 
except  after 
prolonged  and 
patient  atten- 
tion. On  the  other  hand,  there  are  a  certain  few  radiant 
points  from  which,  at  definite  dates,  and  in  great  numbers, 
shooting-stars  emanate  ;  and  it  is  to  these  that  I  will  in  the 
first  instance  direct  the  reader's  attention. 

The  most  important  shower  of  shooting-stars  is  undoubtedly 
that  named  the  Perseids,  because  they  belong  to  the  constella- 
tion Perseus  and  show  themselves  on  or  about  August  10. 


Fig.  235. — Flight  of  Telescopic  Meteors 

(Brooks). 


174  SHOOTING-STARS. 

Meteors  may  be  noticed  some  days  before  and  some  days  after 
the  precise  date  just  mentioned.  They  constitute  a  very  rich 
annual  shower  of  swift  and  bright  meteors,  which  leave  streaks 
behind  them.  The  approximate  centre  of  the  shower  may  be 
taken  to  be  a  point  4°  N.E.  of  the  star  rj  Persei  ;  say,  Right 
Ascension  3  h.  4  m.,  and  Declination  57°  N. 

The  next  most  important  shower  is  that  appertaining  to  the 
constellation  Andromeda,  and  known  as  the  Andromedes,  with 
the  radiant  point  about  4°  N.W.  of  the  star  y  Andromedae  ;  say, 
Right  Ascension  i  h.  40  m.,  and  Declination  44°  N.  Date  : — 
November  27. 

The  third  most  important  shower  may  be  said  to  be  the 
Lyrids,  belonging  to  the  constellation  Lyra,  with  the  radiant 
point  about  85°  S.W.  of  a  Lyrae  ;  say,  Right  Ascension  18  h., 
Declination  33°  N.  These  meteors  move  swiftly,  and  the 
brighter  ones  leave  streaks.  Date  : — April  20. 

The  next  few  paragraphs  will  give  some  of  the  more  im- 
portant showers,  arranged  in  the  order  of  dates  from  January 
onwards. 

January  2,  the  Quadrantids,  belonging  to  the  constellation 
Quadrans.  The  radiant  point  will  be  found  about  12°  N.N.E. 
of  /3  Bootis  ;  say,  Right  Ascension  I5h.  29m.,  and  Declina- 
tion 53°  N.  This  is  a  rich  annual  shower. 

July  28,  the  Aquarids,  belonging  to  the  constellation  Aquarius. 
The  radiant  point  will  be  found  about  5°  N.N.W.  of  8  Aquarii  ; 
say,  Right  Ascension  22  h.  36  m.,  and  Declination  12°  S.  This  is 
an  active  display  of  slow  and  enduring  meteors  which  may  be 
depended  upon  to  recur  annually. 

October  18,  the  Orionids,  belonging  to  the  constellation 
Orion.  The  radiant  point  will  be  found  2°  E.  of  v  Orionis  ;  say, 
Right  Ascension  6h.  8  m.,  and  Declination  15°  N.  This  is  a 
very  rich  shower,  which  occurs  every  year,  and,  though  dated 
for  October  18,  watch  for  it  should  begin  on  October  9,  and  be 
continued  till  October  29. 

November   13,  the  Leonids,  belonging  to  the  constellation 


SHOWERS    OF    METEORS.  175 

Leo.  The  radiant  point  will  be  found  3°  W.N.W.  of  y  Leonis  ; 
say,  Right  Ascension  ioh.,  and  Declination  22°  N.  This  is  a 
great  historic  shower,  which  manifested  sensational  displays  in 
1799,  1833,  and  1866,  and  did  not  reappear  in  its  pristine 
splendour,  as  was  confidently  expected,  in  1899.  A  slight  dis- 
play certainly  belonging  to  this  shower  may  be  expected  every 
year  between  November  9  and  17. 

November  20,  the  Taurids,  belonging  to  the  constellation 
Taurus.  The  radiant  point  will  be  found  5°  N.N.W.  of 
v  Tauri  ;  say,  Right  Ascension  4h.  8m.,  and  Declination  23°  N. 
This  is  a  well-known  shower  of  slow  meteors. 

December  10,  the  Geminids,  belonging  to  the  constella- 
tion Gemini.  The  radiant  point  will  be  found  3°  W.N.W.  of 
a  Geminorum  ;  say,  Right  Ascension  7  h.  22m.,  and  Declina- 
tion 33°  N. 

It  will  be  understood  that  the  showers  enumerated  in  the 
preceding  paragraphs  are  those  which  may  be  regarded  as 
the  most  notable  ;  but,  as  has  already  been  stated,  shooting- 
stars  belonging  to  many  other  groups  may  be  noticed  almost 
every  night  in  the  year.  It  would  take  up  too  much  space 
in  these  pages  to  specify,  and  state  the  positions  of,  even  a 
tithe  of  the  other  recognised  radiant  points  ;  but  observations 
of  luminous  meteors,  small  as  well  as  large,  may  be  suggested 
to  amateurs  as  a  very  interesting  study,  the  fruits  of  which,  if 
collected  and  tabulated  with  care,  will  be  very  useful  in  pro- 
moting the  progress  of  meteoric  astronomy.  Denning  has 
remarked  that  brilliant  meteors  often  emanate  from  the  con- 
stellation Scorpio  in  the  month  of  June.  This  might  be  a 
suggestion  worth  following  up. 

Shooting-stars  often  appear  in  the  pages  of  history,  and 
have  done  so  from  ancient  times.  One  of  the  earliest  allusions 
to  them  dates  from  A.D.  472,  when  we  are  told  by  Theophanes, 
the  Byzantine  historian,  that  the  sky  at  Constantinople  ap- 
peared to  be  on  fire  with  flying  meteors.  A  remarkable  dis- 
play took  place  in  England  and  France  on.  April  4,  1095,  when, 


176  SHOOTING-STARS. 

the   stars   seemed   to  be  "  falling  like  a  shower  of  rain   from 
heaven  upon  the  Earth." 

There  was  a  great  display  on  November  13,  1799,  visible 
throughout  America,  and  of  which  Alexander  Humboldt  has 
left  a  thrilling  narrative  ;  but  the  greatest  display  on  record 
appears  to  have  been  that  of  November  13,  1833,  following 
fine  displays  in  1831  and  1832.  The  1833  shower  was  visible 
over  nearly  the  whole  of  North  America,  and,  from  the  accounts 
which  have  reached  us,  it  must  have  been  one  of  imposing 
grandeur.  In  many  parts  of  the  country  the  population, 
especially  the  Negro  population,  were  terror-stricken,  such 
was  the  beauty  and  magnificence  of  the  spectacle  presented. 
The  following  account  is  from  the  pen  of  a  planter  in  South 
Carolina :  — 

"  I  was  suddenly  awakened  by  the  most  distressing  cries  that 
ever  fell  on  my  ears.  Shrieks  of  horror  and  cries  for  mercy 
I  could  hear  from  most  of  the  Negroes  of  the  three  plantations, 
amounting  in  all  to  about  six  or  eight  hundred.  While  earnestly 
listening  for  the  cause  I  heard  a  faint  voice  near  the  door 
calling  my  name.  I  arose,  and,  taking  my  sword,  stood  at  the 
door.  At  this  moment  I  heard  the  same  voice  still  beseeching 
me  to  rise,  and  saying,  '  O  my  God,  the  world  is  on  fire  ! '  I 
then  opened  the  door,  and  it  is  difficult  to  say  which  excited 
me  the  most — the  awfulness  of  the  scene  or  the  distressed 
cries  of  the  Negroes.  Upwards  of  one  hundred  lay  prostrate 
on  the  ground— some  speechless,  and  some  with  the  bitterest 
cries,  but  with  their  hands  raised,  imploring  God  to  save  the 
world  and  them.  The  scene  was  truly  awful ;  for  never  did 
rain  fall  much  thicker  towards  the  Earth.  East,  west,  north, 
and  south  it  was  the  same." 

Though  I  have  spoken  of  shooting- stars  as  being  visible 
almost  always  everywhere,  this  statement  must  not  be  taken 
to  imply  a  uniform  distribution  over  the  heavens,  because  it 
is  evident  that  in  certain  hours  of  Right  Ascension  (that  is, 
in  the  constellations  occupying  those  hours)  there  are  more 
centres  of  meteor-radiation  than  in  others.  In  other  words, 


RADIANT    POINTS    OF    METEORS. 


177 


that  meteor-centres  are  most  abundant  in  the  first  4  hours 
of  R.A.,  whilst  they  are  fewest  in  the  hours  between  X  and 
XIV  hours.  A  somewhat  similar  disparity  may  be  traced 
in  the  declinations,  there  being  an  obvious  maximum  between 
41°  and  60°  of  North  Declination.  These  results  are  due  to 
the  un- 
tiring in- 
dustry of 
Denning, 
who  is  our 
principal 
meteor 
observer. 
Unfortu- 
nately, no 
c  o  r  r  e  - 
s  p  o  n  d  - 
ing  sta- 
tistics are 
available 
for  the 
Southern 
Hemi- 
sphere, 
becaus  e 
luminous 
meteors 
have 
never 

been  catalogued  and  studied  there  as  they  have  been  in  the 
Northern  Hemisphere.  Dissecting  the  year  by  months,  it 
has  been  found  that  an  overwhelming  preponderance  of 
meteors  are  associated  with  the  month  of  August ;  indeed, 
the  two  months  of  July  and  August  together  provide  50  per 
cent,  of  the  total  number  of  meteors  catalogued  during  the 

12 


Iju 


Fig.  236.— Meteor  Radiant  Point  in  Gemini 
(Dec.  12)  on  Nov.  28— Dec.  9,  1864. 


178  SHOOTING-STARS. 

past  half-century  that  systematic  observation  of  luminous 
meteors  has  been  carried  on. 

The  character  of  a  radiant  point,  and  in  some  sense  the 
details  of  the  observations  which,  under  ordinary  circumstances, 
can  be  carried  out  in  connection  with  it,  will  be  better  realised 
by  an  examination  of  a  plan  (Fig.  236)  showing  the  meteors 
marked  down  on  some  particular  night  as  having  been,  seen 
emanating  from  the  radiant  point  in  question. 

Fig.  234  represents  an  arrangement  devised  by  Mr.  F.  W. 
Longbottom  for  doing  what  he  calls  "fishing  for  meteors." 
He  arranges  in  a  row  several  rapid  cameras  and  takes  his 
chance  of  their  being  able  to  catch  any  meteors  which  may 
show  thtmselves  in  the  regions  of  the  sky  towards  which  the 
cameras  point.  The  stars,  of  course,  are  shown  by  streaks, 
but  that  does  not  matter,  as  their  streaks  can  never  be  mis- 
taken for  the  streak  which  a  meteor  would  leave,  the  difference 
between  the  two  being  always  very  marked.  If  the  time  of 
commencing  and  finishing  the  exposure  is  noted,  a  map  of 
the  stars  recorded  on  the  plate  can  be  made  by  pricking 
off  their  position  on  the  trail  at  any  desired  moment.  It  is 
a  good  plan  to  stop  exposure  when  a  meteor  is  seen  to  cross 
the  field  covered  by  the  camera-lens;  then  the  end  of  each 
star-trail  shows  the  position  of  the  stars  at  the  moment  the 
photograph  was  taken,  just  before  the  actual  attempt.  It  is 
desirable  that  the  exposures  should  be  made  so  that  the  star- 
trails  (or  most  of  them)  begin  and  end  on  the  plate,  though, 
of  course,  near  the  Pole  the  exposure  would  be  long.  The 
time  at  which  the  meteor  is  seen  should  be  noted,  and  also, 
of  course,  any  other  particulars  deserving  to  be  recorded. 

We  will  now  proceed  to  consider  the  question  of  Fireballs. 
It  is  doubtful  whether  any  distinction  of  either  origin  or  nature 
can  properly  be  drawn  between  shooting-stars  and  fireballs, 
or  .that  there  is  any  distinction  at  all  between  them  excepting 
that  of  size,  to  which  perhaps  may  be  added  that  of  duration 
of  visibility.  The  grounds  for  this  assumption  of  identity  of 


PLATE   LXXXI. 


[78! 


FIGS.  238-247 


PLATE    LXXXII. 


NEW  HAVEN.    ., 


PALISADES. 


HAVERFORD 


Meteor  as  seen  at  New  Haven,  Conn.;  Palisades,  N.Y.;  Haverford,  Pa.; 
and  Williamstown,  Mass.,  Nov.  14,  1868. 


First  View. 


Second  View  :    1783,  Aug.  18  (Sanby  and  Robinson). 


1878,  June  7  (Denning). 


1863,  Oct.  19  (Schmidt). 

Fireballs. 


l8o  SHOOTING-STARS. 

origin  and  nature  between  the  two  classes  of  bodies  now  under 
consideration  depend  on  the  fact  that  various  meteor-showers, 
such  as  the  Perseids  and  the  Leonids,  and  many  others, 
whilst  mainly  consisting  of  star-like  points  of  light,  yet  now 
and  again  yield  meteors  of  great  brilliancy,  comparable  alike  in 
size  and  brilliancy  to  the  isolated  objects  which  are  specifically 


I.  2. 

Figs.  252,  253.— Curious  Form  of  Trail  left  by  the  Fireball  of 
Oct.  19,  1877. 

i.  First  effect.  2.  Second  effect  (10  min.  later). 

termed  "  fireballs."  Speaking  generally,  of  course,  it  must  be 
confessed  that  the  large  and  conspicuous  fireballs  of  sufficient 
size  and  importance  to  get  into  the  newspapers  appear  in  the 
heavens  singly,  and,  though  usually  noiseless,  sometimes  are 
seen  to  burst,  making  a  great  noise.  In  this  case  they  are 
generally  pear-shaped.  When  moving  slowly  they  usually  give 


FIRE-BALLS.  l8l 

forth  trains  of  sparks,  which  either  disappear  promptly  or 
sometimes  linger  for  many  minutes,  and  drift  slowly  away, 
apparently  under  the  influence  of  currents  of  wind  high  up  in 
the  atmosphere. 

There  is  a  strong  family  resemblance  between  all  fireballs, 
and  a  drawing  of  one  would  be  typical  of  a  large  number,  as 
will  be  realised  by  an  examination  of  the  illustrations  here 


Fig.  254.— Successive  Changes  in  a  Fireball  during  its  Visibility. 

given.  As  good  a  description  as  could  be  had  of  an  average 
fireball  will  be  found  in  the  following  account  of  one  seen  by 
the  Rev.  T.  W.  Webb  on  November  12,  1861.  He  said  :— 

"We  were  walking,  a  party  of  three  persons,  along  a  wide 
turnpike  road,  fully  lighted  by  a  Moon  10  days  old,  when  we 
were  surrounded  and  startled  by  an  instantaneous  illumination, 
not  like  lightning,  but  rather  resembling  the  effect  of  moon- 
light suddenly  coming  out  from  behind  a  dark  cloud  on  a  windy 


ig2  SttOOTlNG-SfARS. 

night.  It  faded  very  speedily,  but  on  looking  up  we  all  per- 
ceived, at  a  considerable  altitude,  perhaps  60°  or  70°,  a  superb 
mass  of  fire  sweeping  onwards  and  falling  slowly  in  a  curved  path 

down  the  W.S.W. 
sky.  .  .  .  Ruddy 
sparks,  of  the  colour 
of  glowing  coals,  were 
left  behind  at  its 
smaller  end,  and  its 
path  was  marked  by 
a  long  pale  streak  of 
little  permanency. 
Its  termination,  un- 
fortunately, was  con- 
cealed by  boughs  of 
trees,  among  which, 
however,  it  was  traced 
till  possibly  some  10° 
above  the  horizon,  but 
it  had  previously 
undergone  a  great 
diminution.  .  .  .  The 
whole  duration  may 
have  been  as  much 
as  five  seconds.  Its 
aspect  was  decidedly 
that  of  a  lignefied  and 
inflamed  mass,  and 
the  immediate  im- 
pression was  that  of 
rapid  descent." 

The      following 
Fig.  255,-Meteor  of  Nov.  12,  1861         description     of     the 

(w'bb)-  luminous   track   of    a 

large     meteor,     seen 

on  February  22,  1909  (which  seems  to  have  been  indeed  a 
fireball),  and  was  widely  observed  along  the  S.  coast  of 
England,  is  from  the  pen  of  Mr.  C.  G.  Brodie.  The  meteor 
was  quite  unique,  I  think,  in  the  astonishing  length  and 


hn 

£ 


183 


184  SHOOTING-STARS. 

vagaries  of  the  trail  which  it  left  behind.     He  says  that  on  the 
day  in  question — 

"  While  crossing  to  the  Isle  of  Wight  from  Portsmouth,  my 
attention  was  called  to  a  luminous  streak  in  the  southern  sky. 
I  did  not  actually  see  the  meteor,  but  this  must  have  fallen 
about  7.30  p.m.,  as  we  were  leaving  the  harbour.  The  trail, 
when  I  first  saw  it,  extended  from  near  Procyon,  passing  west 
under  a  and  y  Orionis  as  a  plain  luminous  streak  somewhat 
laminated  in  structure.  Passing  from  Wr.  to  S.,  it  entered 
Eridanus,  zigzagging  in  a  curious  fashion,  exhibiting  a  shoulder 
reminding  one  of  a  bayonet,  above  p  Eridani ;  and  then  passing 
S.  and  W.  to  about  <r  Eridani,  where  it  ended  in  a  bluish- 
white,  round,  luminous  nucleus.  From  this  another  streak 
stretched  directly  eastwards,  passing  under  the  two  lower  stars 
of  Orion  (/3  and  /c)  into  Canis  Major  ;  this  streak  was  very  thin. 
The  commencement  of  the  upper  streak  between  Procyon 
and  Orion  next  became  curved  upon  itself,  forming  a  large 
loop,  the  cusp  being  downwards.  Before  we  reached  Ryde 
(say  7.55  p.m.  to  8  p.m.),  the  upper  limb  had  drifted  round 
westwards  into  an  almost  vertical  position,  the  angle  became 
less  acute,  and  the  nucleus  disappeared,  the  lower  streak 
drifting  southwards.  The  whole  trail  had  become  narrower 
and  less  distinct.  As  late  as  8.40,  while  driving  from  the 
Wootton  station,  there  was  still  a  trace  of  the  upright  limb 
in  the  western  sky  in  the  form  of  an  irregular  narrow  streak. 
Several  people  told  me  that  the  fireball  was  so  brilliant  as  to 
resemble  the  sudden  turning  on  of  an  acetylene  lamp  behind 
them.  This  shows  that  the  meteor  must  have  been  exception- 
ally bright,  as  the  sky  was  clear  and  there  was  a  young  Moon. 
The  way  in  which  the  luminous  track  altered  its  position 
suggested  to  my  mind  that  it  was  drifting  by  the  action  of  the 
wind,  which  on  that  day  was  registered  as  S.-E.,  and  the 
day  following  was  still  easterly." 

It  has  been  found  that  certain  dates  may  be  stated  at  which 
fireballs  may  specially  be  looked  for.  The  following  are  some 
of  these  dates:  January  2,  February  7,  April  11-12,  19-20, 
June  6,  July  25-30,  August  7-13,  September  1-2,  6-7,  November 
1-2,  6-9,  11-15,  J9>  27>  December  8,  11-12,  21. 


PATHS    OF    FIRE-BALLS.  185 

Attempts  have  often  been  made  to  subject  particular  fire- 
balls to  computation  as  regards  their  distances,  sizes,  and 
velocities  ;  but  the  suddenness  of  their  appearance,  and  the 
rapidity  of  their  movements  and  of  the  changes  which  they 
undergo  render  the  results  in  all  cases  very  uncertain.  Subject 
to  this  view  it  may  be  stated  that  their  height  above  the 
Earth's  surface  commonly  varies  between  a  few  miles  up  to 
80  miles  or  more  ;  their  absolute  diameter  between  perhaps 
50  yards  and  2  miles;  and  their  velocity  between  2  miles  and 
40  miles  per  second.  The  foregoing  figures  are  actual  results 
in  the  case  of  particular  fireballs.  It  may  be  remarked,  how- 
ever, that  one  is  apt  to  exaggerate  estimates  of  diameter,  and 
also  of  velocity,  measured  in  the  first  instance  as  so  many 
degrees  in  the  sky  in  so  many  minutes.  The  only  cases  in 
which  trustworthy  results  can  be  assured  are  in  the  instances, 
naturally  very  rare,  in  which  two  trained  observers  in  widely 
separated  parts  of  the  country  may  each  have  the  good 
fortune  to  see  the  same  fireball  start  on  its  career  and  be 
able  to  follow  it  to  the  end.  There  are  a  few  instances  of  this 
on  record,  and  the  calculated  results  may  in  such  cases  be,  to 
a  large  extent,  depended  upon. 

There  must  now  be  mentioned  a  matter  connected  with 
celestial  mechanics,  which  might  with  equal  propriety  be 
attached  to  the  chapter  on  comets  or  to  this  one  on  meteors. 
I  allude  to  the  modern  discovery  of  the  association  between 
certain  comets  and  certain  displays  of  luminous  meteors. 
This  may  now  be  regarded  as  a  clearly  ascertained  fact,  though 
it  is  far  from  easy  to  pronounce  dogmatically  on  the  circum- 
stances so  far  as  they  are  yet  known.  The  simple  fact,  concisely 
expressed,  is  that. there  are  meteor-showers  revolving  round  the 
Sun  in  orbits  so  closely  resembling  the  orbits  of  certain  comets 
that  we  are  driven  to  the  startling  conclusion  that  some  of  the 
recognised  meteor-showers  are  either  off-shoots  from  comets 
or  are  the  actual  materials  of  disintegrated  comets.  There  is, 
at  any  rate,  one  instance  of  this  which  is  hardly  open  to  serious 


1 86  SHOOTING-STARS. 

question.  The  former  well-known  Comet  of  Biela  has  abso- 
lutely disappeared,  but  there  exists  a  swarm  of  meteors 
travelling  round  the  Sun  which  present  themselves  every 
November,  radiating  from  the  constellation  Andromeda, 
which  pursue  a  path  practically  identical  with  that  which  used 
to  be  followed  by  Biela's  Comet,  so  long  as  we  knew  it  as  a 
comet ;  and  the  conclusion  is  inevitable  that  the  comet,  as  it 
originally  was,  has  been  broken  up  and  become  a  swarm  of 
meteors. 

Whilst  it  is  obvious  that  such  a  conclusion  sets  us  all 
thinking,  it  is  not  easy  to  say  how  far,  or  in  what  direction, 
our  thoughts  ought  to  go. 

The  following  is  a  summary  statement  of  the  association  of 
certain  comets  with  certain  meteor-showers  : 


Comet. 

Tebbutt's 
Halley's 
1862  (iii.) 
Tempel's  1866  (i.) 
Biela's 

Meteors. 
Lyrids 
Aquarids 
Perseids 
Leonids 
Andromedes 

Radiant  Point. 

Lyra 
Aquarius 
Perseus 
Leo 
Andromeda 

Date. 

April  20 
May  1-6 
Aug.  10-12 
Nov.  13 
Nov.  27 

The  circumstances  of  Tempel's  Comet  are  specially  remark- 
able, and,  as  they  have  been  investigated  very  fully  by  Kirk- 
wood,  some  details  will  interest  the  reader.  It  has  already  been 
stated  in  an  earlier  part  of  this  chapter  that  the  Leonid  meteors 
first  attracted  the  attention  of  a  scientific  observer  in  1799,  and 
that  at  a  subsequent  date  it  was  clearly  ascertained  that  the 
shooting-stars  seen  in  1799,  1833,  and  1866  were  periodic 
manifestations  of  the  same  shower  ;  but  it  was  not  till  near  the 
last-named  date  that  the  association  of  a  certain  comet  with  this 
shower  became  fully  understood. 

The  subject  was  started  in  its  first  developement  by  the  dis- 
covery, on  December  19,  1865,  of  a  small  comet  by  Tempel,  then 
at  Marseilles.  It  was  generally  observed  for  7  weeks,  and, 
although  not  a  very  conspicuous  object,  its  relations  to  the 


THE    LEONID    METEORS. 


i87 


Earth  and  Uranus  may  be  said  to  have  given  it  an  importance 
surpassed  by 
very  few 
comets.  The 
final  computa- 
tion of  its 
orbit  showed 
that  it  was  a 
period  ic  al 
comet  revolv- 
ing round  the 
Sun  in  33'28 
years.  This 
comparatively 
short  period 
led  to  cata- 
1  ogue  s  of 
comets  being 
searched,  and 
it  was  found 
that,  reckon- 
ing backwards 
33 '28  years  a 
good  many 
times,  there 
were  coinci- 
dences (with 
breaks)  back 
to  the  year 
465  B.C.  of 
comets  which 
might  be 
identical.  If 
one  can 
assume  that  such  a  date  may  be  safely  taken  as  a  terminus  a 


Fig.  257. — Orbit  of  the  Leonids  of  Nov.  13  and 
of  the  Comet  of  1866  (i)  relatively  to  the 
Orbit  of  Certain  Planets. 

Points  on  the  orbit  opposite  to  the  letters   A,  B,  C   are   the 
positions  of  the  3  detached  swarms,  according  to  Kirkwood 


1 88  SHOOTING-STARS. 

quo,  we  have,  as  a  result,  72  periods  of  33*28  years  down  to 
A.D.  1366.  A  comet  in  1366  is  regarded  as  another  absolutely 
certain  terminus  a  quo  for  later  centuries.  From  1366  to  1866 
is  499*3  years,  or  fifteen  periods  of  33*28  years. 

Professor  H.  A.  Newton,  working  on  independent  lines,  traced 
back  the  great  showers  of  1866  and  1833  to  A.D.  902.  He 
showed  that  there  were  five  possible  periods  for  the  revolution 
of  the  swarm  round  the  Sun,  namely,  180  days,  185  days,  355 
days,  377  days,  or  33^  years.  This  important  uncertainty  was, 
however,  first  definitely  solved  by  Professor}.  C.  Adams  in  1867, 
who,  by  working  on  Newton's  labours,  found  definitely  that  the 
periodic  time  was  about  33*25  years. 

The  conclusion  that  Tempel's  Comet  and  the  great  meteoric 
swarm  of  1866  and  previous  dates  move  in  the  same  orbit,  and 
that  the  swarm  of  meteors  was  in  fact  derived  from  the  comet, 
was  reached  almost  simultaneously  by  Peters,  Le  Verrier,  and 
Schiaparelli  ;  but  the  matter  was  carried  a  good  deal  farther  by 
Kirkwood,  who  found  very  clear  proofs  not  only  of  a  second,  but 
also  of  a  third  cluster  belonging  to  the  same  family,  moving  in 
orbits  clearly  identical  in  form  with  those  of  the  comet  and  the 
1866  meteors.  It  need  hardly  be  pointed  out  what  an  interest- 
ing series  of  coincidences  have  thus  been  brought  to  light.  I 
have  not  space  to  go  into  further  details,  but  Kirkwood  gathered 
up  from  a  long  series  of  observations  of  meteor-showers,  spread 
over  several  centuries  in  each  case,  materials  which  furnished 
him  with  the  information  on  which  he  based  his  conclusions. 


We  will  pass  now  to  the  consideration  of  aerolites,  and  this 
brings  us  face  to  face  with  the  important  questions  which  I 
have  not  yet  broached  :  What  is  a  shooting-star  ?  What  is  a 
fireball  ?  Whence  comes  an  aerolite  ?  I  think  it  must  be 
said  that  these  questions  must  be  answered  together,  and  that 


AEROLITES.  189 

the  conjoint  answer  must  be  that  all  these  bodies  are,  or  have 
been,  masses  of  solid  matter  floating  about  in  space,  coming 
from  whence  we  know  not,  but  which,  when  they  reach  the 
Earth's  atmosphere  at  about  80  miles  above  the  Earth's  surface, 
(i)  take  fire  and  fizzle  away,  or  (2)  take  fire  and  burst,  or 
(3)  fall  to  the  ground  as  solid  masses  of  stony  matter,  which  are 
either  in  their  original  form  and  of  their  original  size,  or  which, 
when  we  see  them  on  the  ground,  are  the  broken-up  fragments 
of  some  larger  mass,  which  has  become  disintegrated,  either  in 
the  upper  regions  of  our  atmosphere  or  farther  off  in  Space. 

With  aerolites  we  rather  pass  from  the  domain  of  astronomy 
into  that  of  chemistry,  geology,  mineralogy,  and  geography,  and 
therefore  my  treatment  of  the  subject  in  these  pages  must  be 
brought  into  somewhat  narrow  limits.  The  crucial  fact  which 
we  have  to  bear  in  mind  is  that  now  and  again  stony  or  semi- 
metallic  masses,  composed  of  many  diverse  materials,  fall  on  the 
Earth,  from  whence  coming  we  know  not. 

The  number  of  such  falls,  recognised  as  such,  has  now  reached 
a  considerable  total,  and  covers  a  large  field  both  in  time  and 
area  ;  that  is  to  say,  that  instances  of  such  falls  have  been 
recorded  at  many  dates,  beginning  with  more  than  2000  years 
ago  ;  and  the  produce  of  such  falls  may  be  found  in  every  part 
of  the  habitable  globe.  But  many  aerolites  have  been  trans- 
ported by  the  hand  of  man  from  the  place  where  they  fell  to 
some  neighbouring  or  distant  public  museum.  Hence  it  comes 
about  that  specimens  of  aerolites  are  to  be  found  alike  in  the 
British  Museum  and  in  many  other  public  museums  in  different 
parts  of  the  world.  Naturally,  most  of  the  aerolites  which  have 
been  found  were  in  the  stone-cold  condition,  and  their  extra- 
terrestrial origin  had  to  be  inferred  from  analogy  and  chemical 
analysis  ;  but  a  few  cases  are  on  record  in  which  the  aerolite 
was  seen  to  fall,  and  was  examined  by  an  eye-witness  and 
found  to  be  still  warm.  The  following  is  a  typical  case  in  point. 
On  April  20,  1876,  a  mass  of  meteoric  iron  weighing  about 
7  Ibs.  fell  at  Rowton,  in  Shropshire.  We  are  told  that  shortly 


190  SHOOTING-STARS. 

before  4  p.m.  a  sound  like  that  of  thunder,  followed  by  reports 
as  of  cannon,  shook  the  air,  and  was  heard  during  rain-showers 
for  many  miles  round  in  that  neighbourhood.  No  fireball  was 
observed.  The  iron  was  found  about  an  hour  afterwards  in  a 
meadow,  where  it  had  sunk  into  the  earth  to  a  depth  of  18 
inches.  When  dug  out  it  was  still  quite  hot. 

In  the  foregoing  case  the  material  was  metallic,  more  or  less. 
But  in  other  cases,  and  the  majority,  the  material  has  been 
generally  stone  of  sorts,  either  a  conglomerate  mass  of  mixed 
composition  or  a  mass  somewhat  basaltic  in  its  nature.  It  is 
obvious  that  opportunities  for  actually  observing  the  fall  of  an 
aerolite  are  few  and  far  between,  and  that  the  most  which  we 
can  do  is  to  study  their  appearance  and  investigate  their 
chemical  composition  in  the  light  of  the  facts  gathered  up  for 
us  as  regards  the  time  and  place  of  their  fall. 


CHAPTER   XI. 
THE  STARS. 

The  apparent  movement  of  the  stars  on  a  starlight  night. — The  stars 
in  magnitudes. — Diurnal  movement  of  the  Earth. — Its  conse- 
quences.— The  stars  visible  vary  with  the  latitude. — The  expression 
"fixed  stars." — Stars  that  are  visible  to  the  naked  eye. — The 
identification  of  the  stars. — Bayer's  system  of  lettering  stars. — 
Flamstecd's  numbers. — Sir  J.  HerscheVs  striking  remarks. — Total 
number  of  naked-eye  stars. — Amount  of  star-light. — Twinkling. — 
Double  stars. — Binary  stars. — Coloured  stars. — Complementary 
colours. — Triple  and  multiple  stars. — Variable  stars. — Notable 
variable  stars. — Temporary  stars. — Tycho  Brake's  Star. — Recent 
temporary  stars. 

WE  are  now  starting  on  what  is  obviously  a  very  large  subject, 
and  one  which  has  numerous  ramifications,  and  I  propose  to 
treat  the  sequence  of  the  different  branches  somewhat  in  the 
order  in  which  the  student  of  the  stars  would  be  likely  to 
approach  the  subject,  first  of  all  as  an  observer  using  only  his 
eyes,  and  then  proceeding  to  employ  an  opera-glass,  a  small 
telescope,  and  a  larger  telescope  all  in  succession.  The 
dominant  idea  which  will  run  as  a  thread  through  this  and  the 
later  chapters  dealing  with  the  constellations  will  be  that  the 
reader  will  wish  to  make  himself  acquainted  with  the  actual 
geography  (though  this  is  not  the  proper  word !)  of  the  heavens, 
with  the  view  of  knowing  what  interesting  objects  to  look  for 
and  where  to  find  them. 

1  Jt  should  be  "  uranography,"  from  Oupai/os  heaven,  and  ypa^w,  I  write. 
191 


192  THE    STARS. 

I  will  now  proceed  to  deal  with  a  variety  of  general  con- 
siderations relating  to  the  stars,  individually  and  collectively, 
including  their  apparent  movements  through  the  different 
seasons  of  the  year.  Some  of  these  topics  may  seem  to  be  dry, 
but  clear  conceptions  as  to  many  of  them  are  of  prime  im- 
portance. 

Everybody,  I  suppose,  knows  that  the  Earth  turns  on  its  axis 
as  a  wheel  turns  on  its  axle.  The  visible  consequences  of  this 
act  should  be  thoroughly  realised,  and  this  will  best  be  done 
by  the  reader  taking  his  station  on  a  clear,  starlight  night  in 
some  high  and  fairly  open  position  facing  the  N.,  but  with 
a  tolerably  wide  range  of  view  all  round.  Let  him,  in  the 
first  instance,  try  and  fix  in  his  mind  the  grouping  of  the  stars 
in  the  W.,  somewhere  about  the  point  where  the  Sun  has 
set.  Next  let  him  turn  his  eyes  and  take  note  of  the 
stars  immediately  overhead.  Finally,  let  him  examine  the 
stars  due  E.  of  his  position,  and  fix  in  his  mind  their  general 
appearance. 

Having  taken  stock,  as  it  were,  of  these  three  portions  of 
the  heavens,  let  him  go  indoors  for  an  hour,  or,  better  still,  for 
a  couple  of  hours,  and  then  come  out  again  and  refresh  his 
memory  by  trying  to  regain  the  conceptions  of  two  hours  ago  ; 
and  he  will  find  some  difficulty  in  doing  so.  Several  of  the 
principal  stars  which  he  had  previously  noted  as  low  down  in 
the  western  horizon  will  have  disappeared.  Those  which  had 
been  overhead  will  have  appreciably  moved  on  towards  the 
W.,  whilst,  when  he  directs  his  eyes  to  the  eastern  horizon, 
he  will  discover  a  fresh  set  of  stars  which  he  had  not  seen 
before,  those  which  he  had  seen  having  visibly  risen  higher  up 
towards  the  zenith. 

If,  instead  of  coming  out  a  second  time  the  same  evening,  the 
reader  had  postponed  for  a  week  his  second  inspection  of  the 
heavens,  he  would  have  noticed  very  material  changes  in 
the  aspect  of  affairs.  Every  group  of  stars  would  have  moved 
on  ;  those  which  had  been  in  the  W.  would  have  dis- 


APPARENT    MOVEMENTS    OF    THE    STARS. 


193 


appeared,  and  a  new  assortment  would  have  started  up  in  the 
east.  If,  instead  of  resuming  his  work  in  a  week,  he  had 
waited  a  month,  the  changes  in  the  aspect  of  the  sky  would 
have  been  still  more  radically  different ;  and,  to  cut  a  long  story 
short,  if  he  had  prolonged  his  study  of  the  sky  by  only  looking 
at  it  once  a  month  for  12  months,  he  would,  at  the  end  of 
the  twelfth  month,  have  seen  all  the  stars,  and  in  identically 


Fig.  259.— Apparent  Changes  in  a  Group  of  Stars  in  the  Course 
of  12  hours  between  Rising  and  Setting. 


the  same  positions  in  which  they  had  been  on  the  night  of  his 
first  view   one  year  previously.      Otherwise   expressed,   what 
would  have  happened  would  have  been  this  :  he  would  have 
had    under    notice    all  the    constellations,   and   therefore    all 
the  stars,  which  under  any  possible  circumstances   could  be 
seen  in  the  latitude  of  his  place  of  observation. 
This  mention  of  the  word  "  latitude  "  opens  up  a  subsidiary 
13 


194  THE    STARS. 

matter  of  great  practical  importance.  In  consequence  of  the 
axis  of  the  Earth  being  inclined  about  23°  to  the  Ecliptic  (the 
apparent  annual  path  of  the  Sun),  the  whole  body  of  stars  need 
to  be  considered  under  three  heads  : — 

1.  Those  in  the  neighbourhood  of  the  Poles  which  never  go 
below  the  horizon,  but  which  are  visible  on  every  clear  night 
throughout  the  year. 

2.  Those  which  I  have  first  described,  which  come  into  view 
and  pass  out  of  view,  being  obliterated  in  turn  by  the  Sun's 
rays  as  the  Sun  in  its  annual  course  passes  through  the  signs 
of  the  Zodiac  ;  and, 

3.  Those   which   lie  towards  the  S.,  including  those  which 
gather   round   the    South   Pole,  all  of  which   are   perpetually 
concealed  from  the  observer  in  a  given  northern  latitude. 

The  foregoing  statement  respecting  the  visibility  of  particular 
constellations  and  stars  needs  a  twofold  extension.  In  the 
first  place,  if  the  observer  in  the  first-mentioned  latitude — sup- 
pose we  say  London— travels  to  the  North  of  Scotland,  he  will 
lose  some  of  the  stars  which,  in  the  •  latitude  of  London,  he 
glimpsed  when  they  were  passing  along  his  extreme  southern 
horizon. 

If,  on  the  other  hand,  he  moves  away  from  London  to  the 
extreme  South  of  France,  he  will  find,  travelling  along  his 
southern  horizon,  stars  of  the  existence  of  which  he  had 
obtained  no  knowledge  when  at  his  original  station  in  the 
latitude  of  London.  If  he  should  proceed  farther  S.,  right 
away  6000  miles  to  the  Cape  of  Good  Hope,  or  on  to  Australia, 
he  will  come  face  to  face  with  an  entire  reversal  of  everything 
which  he  had  seen  when  in  the  latitude  of  London.  The 
North  Pole,  the  Great  Bear,  the  Little  Bear,  and  all  the 
constellations  in  their  neighbourhood  would  have  disappeared 
irrecoverably.  The  constellations  which  had  passed  over  the 
zenith  in  London  will  be  low  down  in  the  northern  horizon, 
the  previously  visible  North  Pole,  and  its  Pole-star,  will  have 
disappeared,  and  been  replaced  by  another  Pole,  and  another 


THE    STARS    AS    SEEN    IN    DIFFERENT    LATITUDES.        195 

Pole-star,1  and  an  entirely  new  set  of  constellations  will  pass 
over  the  zenith  at  the  Cape  and  in  Australia,  so  that  in  point 
of  fact  the  aspect  of  the  nocturnal  heavens  will  have  become 
completely  revolutionised. 

The  statement  just  made  as  regards  the  consequences  of 
an  observer  transferring  himself  from  London,  in  the  North 
latitude  of  51°,  to  a  place  in  the  corresponding  latitude  in  the 
Southern  Hemisphere,  which  would  be  somewhat  to  the  S. 
of  New  Zealand,  may  be  otherwise  expressed  thus  :  that  the 
stars  which  are  within  the  "circle  of  perpetual  apparition," 
otherwise  known  as  "  circumpolar  stars,"  and  are  therefore 
perpetually  visible  in  England,  will  be  perpetually  invisible  in 
New  Zealand,  and  the  stars  which  are  perpetually  out  of  view 
in  England  will  be  perpetually  in  view  in  New  Zealand.  It 
must  be  understood  that  this  statement,  to  be  literally  true  in 
substance,  depends  on  identical  latitudes  being  compared,  and 
that  the  latitude  of  51°,  which  is  assumed  to  be  that  of  London, 
finds  its  literal  counterpart  not  actually  in  New  Zealand,  but 
a  little  distance  S.  of  the  most  southerly  point  of  New 
Zealand. 

I  hope  that  the  foregoing  statements  as  to  the  changes  in 
the  aspects  of  the  heavens  which  will  be  noticed  by  an  observer 
watching  the  stars  from  night  to  night  throughout  a  period  of 
one  year  will  be  sufficiently  intelligible  ;  and  that  what  is  meant 
is  that  the  whole  vault  of  heaven  with  its  myriads  of  fixed  stars 
is  in  constant  movement  as  an  unchanging  whole.  But  this 
presentation  of  the  matter,  though  convenient  and  indeed 
necessary  to  convey  general  ideas,  is  not  quite  literally  true  ; 
it  is  one  of  those  conventional  untruths  which  are  often  useful 
in  astronomy  as  a  preliminary  to  pave  the  way  to  precise 

1  Whilst  the  Northern  Hemisphere  has,  as  its  representative  Pole-star,  a 
fairly  bright  star  (a  Ursa  Minoris),  which  is  very  close  to  the  exact  polar 
point,  it  is  to  be  regretted  that  the  South  Pole  has  no  sufficient  Pole-star,  the 
nearest  star  to  the  South  Pole  (<r  Octantis)  being  only  of  magnitude  5,  and 
some  distance  from  the  polar  point." 


196  THE   STARS. 

accuracy.  The  term  "  fixed  stars  "  is  so  old  and  so  universally 
used  that  I  think  it  may  be  said  to  deceive  nobody.  Moreover, 
it  is  perfectly  well  known  that  certain  objects  which  are  often 
colloquially  included  under  the  name  of  "  stars  "  are  not  fixed, 
but  wander  hither  and  thither,  and  are  known  as  "planets," 
which  very  word  itself  implies  that  they  do  not  occupy  fixed 
positions.1  Furthermore,  precise  modern  observations,  con- 
ducted with  special  skill  and  care,  have  brought  to  light  the 
fact  that  a  very  considerable  number  of  stars  are  endued  with 
actual  proper  motion  of  their  own,  so  that  they  move  relatively 
to  one  another,  though  by  amounts  which  are  entirely  beyond 
the  grasp  of  the  naked  eye. 

The  stars  being  of  different  apparent  size,  which  for  our 
present  purpose  means  brilliancy,  have  been  classified  in  magni- 
tudes which  range  from  the  1st  to  the  i8th,  though  the  higher 
figures  which  one  meets  with  in  various  astronomical  publica- 
tions are  very  uncertain  and  fanciful. 

It  is  usually  considered  that  the  range  of  naked-eye  vision  ends 
with  the  6th  magnitude  inclusive  ;  but  with  many  persons  the 
limit  must  be  put  at  5^,  whilst  with  a  few  other  people  it  may 
be  extended  to  6|.  Beyond  this  the  range  goes  to  7,  8,  9,  10, 
n,  and  12;  and  there  all  accurate  values  may  be  deemed  to 
cease,  though  one  often  comes  upon  higher  figures.  All  the 
recognised  figures  began  with  eye  estimations  in  bygone  times. 
It  is  obvious  that  this  is  a  most  unsatisfactory  and  unbusiness- 
like way  of  estimating  the  brightness  of  a  star,  and,  though 
organised  photometric  methods  have  often  been  proposed,  they 
have  only,  up  till  now,  been  carried  out  to  a  limited  extent. 
The  observers  at  Harvard  College,  United  States,  have  pub- 
lished catalogues  of  naked-eye  stars  estimated  in  brightness 
by  means  of  an  instrument  called  a  photometer,2  and  the  value 
of  their  labours  is  very  great  indeed. 

Independently  of  instrumental  values  of  star-magnitudes,  it 

1  Gr.  7r\avrjr>)s,  a  wanderer. 

"  Gr.  $u>s,  light,  and  pirpov,  a  measure. 


THE    CLASSIFICATION    OF    STARS.  197 

is  customary  to  subdivide  magnitudes  decimally  from  o  to  9, 
which  gives  an  air  of  exactitude  to  the  figures  assigned,  which 
can  only  be  regarded  as,  in  many  cases,  a  sham. 

When  we  come  to  deal  with  the  stars  in  detail  it  will  be  seen 
that  other  classifications  besides  those  depending  on  brilliancy 
have  to  be  resorted  to  ;  so  that  we  shall  have  to  put  into 
separate  sections  "  coloured  stars,"  "  double  stars,"  "  temporary 
stars,"  "  variable  stars,"  and  "  moving  stars."  Next  will  follow, 
as  a  complement  to  double  stars,  "  triple,"  "  quadruple,"  and 
"  multiple  stars,"  clusters  of  stars,  and  nebulae,  and  last,  but 
not  least,  the  Milky  Way.  But,  before  entering  on  such  details, 
there  are  several  other  matters  which  must  be  brought  under 
the  notice  of  the  reader. 

Postponing  a  consideration  of  the  constellations  to  the  chapter 
specially  dedicated  to  them  it  will  yet  be  convenient  in  this 
chapter  to  say  something  about  the  identification  of  the  stars. 
In  early  times,  after  a  targe  number  of  the  important  constella- 
tions had  been  named  (and  the  origin  of  most  of  these  names 
is  lost  in  antiquity),  it  soon  came  into  men's  minds  that  some 
means  of  distinguishing  one  star  from  another  in  the  same 
constellation  was  urgently  necessary.  This  was  a  matter  taken 
in  hand  by  the  Arabian  astronomers  during  the  centuries 
following  the  Christian  era.  Most  of  the  names  of  particular 
stars  now  in  use  (Aldebaran,  Altair,  etc.)  are  of  Arabic  origin, 
with  additions  of  Greek  and  Latin  origin  (Arcturus,  Spica 
Virginis,  etc.).  These  names  served  their  purpose  in  a  certain 
way,  and  for  a  certain  time,  but  the  need  of  more  precise  names 
was  soon  felt,  hence  Aldebaran  came  to  be  called  Oculus  Tauri, 
the  "eye  of  the  bull/5  a  phrase  supposed  to  give  some  indica- 
tion of  where  the  star  was  to  be  found. 

It  requires  no  great  amount  of  acuteness  to  realise  that 
such  methods  to  indicate  stars  as  these  were  so  rough  and 
vague  as  to  be  practically  useless  ;  but  a  very  marked  ad- 
vance in  the  direction  of  scientific  exactness  was  made  in 
1603  by  a  German  astronomer  named  Bayer,  who  in  that 


198  THE    STARS. 

year  published  the  first  Celestial  Atlas,  the  title  of  which 
was  Vranoinetria,  Omnium  Asterismorum  continens  Sche- 
mata Novd  Methodo  delineata.  In  this  work  the  stars  of 
each  constellation  were  distinguished  by  having  attached 
to  them  the  letters  of  the  Greek  alphabet,  and  these  have 
been  used  ever  since.  It  would  seem  that  Bayer  started 
with  the  idea  that  he  would  label  the  stars  in  the  order  of 
brightness  from  a  and  /3,  and  so  downwards  as  far  as  might  be 
necessary  till  the  alphabet  was  exhausted.  The  common  idea 
is  that  the  order  of  the  alphabet,  as  we  know  it,  did  and  does 
represent  the  order  of  the  stars  so  estimated  ;  and  occasionally 
it  has  been  argued  that  the  brightness  of  a  star  must  have 
varied,  because  it  does  not  occupy  its  proper  position  in  bright- 
ness according  to  its  position  in  the  Greek  alphabet.  There 
is,  however,  no  doubt  that  such  an  argument  is  worthless,  and 
that  the  idea  of  accurate  sequence  cannot  be  carried  further 
than  to  say  that  the  brightest  star  in  every  constellation  always 
had  a  allotted  to  it,  and  perhaps  the  second  brightest  ft  but 
that  all  the  rest  followed  somewhat,  but  perhaps  not  altogether, 
at  haphazard. 

The  next  worker  in  this  field  was  our  own  John  Flamsteed, 
once  Astronomer  Royal.  He  prepared  and  in  1725  published 
his  Catalogus  Britannicus,  which  contained  3310  stars 
observed  at  Greenwich,  and  reduced  to  1690,  all  the  stars 
of  which  were  numbered  by  his  modern  editor,  Francis  Baily, 
from  No.  i  onwards  in  each  constellation.  Flamsteed's  num- 
bers are  still  in  general  use,  and  they,  together  with  Bayer's 
Greek  letters,  are  to  be  found  engraved  in  almost  every  star- 
atlas  in  existence.  When  Bayer's  letters  are  used  they  are 
prefixed  to  the  genitive  case  of  the  Latin  name  of  the  con- 
stellation, thus  :  a  Ursae  Majoris,  /3  Canis  Minoris,  and  so  on. 
In  addition  to  Bayer's  Greek  letters  and  Flamsteed's  numbers 
there  are  a  few  stars  indicated  by  Roman  letters.  The  use 
of  these  letters,  but  to  a  very  limited  extent,  was  really  started 
before  Bayer's  time  by  an  Italian,  Piccolomini  of  Siena,  but 


SIR    J.    HERSCHEL    ON    THE   STARS    GENERALLY.         199 

his  use  of  them  was  limited.  A  long  time  elapsed  after  the 
invention  of  the  telescope,  and  the  commencement  of  methodical 
observations  of  stars  as  regards  their  exact  places  in  the 
heavens,  before  the  constellations  and  stars  of  the  Southern 
Hemisphere  were  submitted  to  critical  instrumental  measure- 
ment. 

This  did  not  come  about  till  Lacaille  published,  in  1763,  his 
Cesium  Australe  Stelliferum,  which  contains  1943  southern 
Stars,  observed  by  him  at  the  Cape.  Lacaille  had  the  whole 
Southern  Hemisphere  to  himself,  so  to  speak,  and  he  turned 
his  opportunities  to  account  not  only  by  observing  its  stars  but 
also  by  attaching  letters,  Greek  and  Roman,  to  them,  at  the 
same  time  creating  14  new  southern  constellations.  In  the 
particular  case  of  the  constellation  Argo,  one  of  vast  extent 
and  with  many  large  stars,  Lacaille  got  into  a  good  deal  of 
difficulty  in  the  lettering — that  is  to  say  in  finding  letters  for  the 
1 80  stars  to  which  he  deemed  it  desirable  to  attach  letters. 
Thus  it  came  about  that,  besides  using  up  the  Greek  alphabet, 
he  employed  the  whole  of  the  Roman  alphabet,  both  in  capital 
and  small  letters,  repeating  indeed  each  several  times,  and  so, 
of  course,  paving  the  way  for  a  good  deal  of  confusion. 

Sir  John  Herschel  once  made  some  remarks  on  the  subject 
of  the  stars  which  are  so  very  striking  as  to  deserve  quotation, 
the  more  so  as  they  help  to  indicate  the  utilitarian  side  of 
astronomy,  and  moreover  constitute  what  the  French  call 
politely  a  dementi  to  the  absurd  statement  once  made  by  the 
late  Sir  George  Cornwall  Lewis  that  astronomy  is  only  a  science 
of  "  pure  curiosity."  These  are  Sir  John's  words  : — 

"  The  stars  are  the  land-marks  of  the  universe,  and,  amidst 
the  endless  and  complicated  fluctuations  of  our  system,  seem 
placed  by  its  Creator  as  guides  and  records,  not  merely  to 
elevate  our  minds  by  the  contemplation  of  what  is  vast,  but  to 
teach  us  to  direct  our  actions  by  reference  to  what  is  immutable 
in  His  works.  It  is  indeed  hardly  possible  to  over-appreciate 
their  value  in  this  point  of  view.  Every  well-determined  star, 


200  THE    STARS. 

from  the  moment  its  place  is  registered,  becomes  to  the 
astronomer,  the  geographer,  the  navigator,  the  surveyor,  a 
point  of  departure  which  can  never  deceive  or  fail  him,  the 
same  for  ever  and  in  all  places,  of  a  delicacy  so  extreme  as 
to  be  a  test  for  every  instrument  yet  invented  by  man,  yet 
equally  adapted  for  the  most  ordinary  purposes  ;  as  available 
for  regulating  a  town  clock  as  for  conducting  a  navy  to  the 
Indies  ;  as  effective  for  mapping  down  the  intricacies  of  a 
petty  barony  as  for  adjusting  the  boundaries  of  transatlantic 
empires.  When  once  its  place  has  been  thoroughly  ascertained 
and  carefully  recorded,  the  brazen  circle  on  which  that  useful 
work  was  done  may  moulder,  the  marble  pillar  totter  on  its  base, 
and  the  astronomer  himself  survive  only  in  the  gratitude  of  his 
posterity ;  but  the  record  remains,  and  transfuses  all  its  own 
exactness  into  every  determination  which  takes  it  for  a  ground- 
work, giving  to  inferior  instruments,  nay,  even  to  temporary 
contrivances,  and  to  the  observations  of  a  few  weeks  or  days,  all 
the  precision  attained  originally  at  the  cost  of  so  much  time, 
labour,  and  expense." 

As  regards  the  number  of  the  stars  there  is  great  mis- 
apprehension in  the  minds  of  many  people.  One's  natural 
impulse  is  to  exaggerate  the  numbers.  Bearing  in  mind  the 
difficulty  of  drawing  precise  lines  of  demarcation  between 
the  different  magnitudes  (the  difference  between  the  ist  and 
the  2nd  not  excepted),  the  following  may  be  stated  as 
approximately  the  numbers  for  the  several  magnitudes  : — 

Magnitudes.  No.  of  Stars. 

1st    .                   ,         .          .         .  .          21 

2nd  .         ...         .         .  .         65 

3rd   .         ...         .         .  -       190 

4th  .        <v        .        ....  -425 

5th   .         .         .         .        .         .  .1100 

6th .     3200 

Below  the  6th  magnitude  the  uncertainties  are  too  great  to 
make  exact  estimates  justifiable,  and  it  is  not  safe  to  say  more 
than  that  the  visible  stars,  from  the  ist  magnitude  down  to  the 
9th  inclusive,  have  been  estimated  by  experienced  observers 


STATISTICS    OF    THE    STARS.  2OI 

to  be  about'  130,000  in  number,  though  Argelander  raised  this 
figure  to  200,000. 

It  is  generally  considered  that  the  total  number  of  stars 
visible  to  the  naked  eye  in  England  on  any  given  night  must 
not  be  put  higher  than  2500,  whilst  the  grand  total  of  all  the 
stars  which  could  be  counted  in  England,  all  the  months 
lumped  together,  may  be  said  to  be  no  more  than  about  4000, 
though  Heis,  of  Miinster,  turned  this  into  5000. 

Such  statistics  as  these  are  not  very  profitable,  because 
different  enumerators  are  certain  to  do  their  work  of  taking 
a  census  of  the  stars  on  different  principles  :  still,  the  subject 
could  not  be  entirely  passed  over. 

A  question  which  has  been  raised,  though  it  can  hardly  be 
said  to  have  been  settled,  on  any  sure  basis,  is  the  question 
whether  the  stars,  or  any  of  them,  transmit  any  measurable 
quantity  of  heat.  Experiments  carried  out  many  years  ago  at 
the  Greenwich  Observatory  and  elsewhere  seem  to  suggest  an 
affirmative  answer,  but  when  I  quote  one  of  the  results  in  the 
form  in  which  it  was  announced,  scepticism  on  the  subject  will 
not  be  deemed  unreasonable.  Here  is  this  result :  That 
Arcturus,  at  an  altitude  of  25°  above  the  horizon,  was  found  to 
emit  the  same  amount  of  heat  as  that  which  would  be  felt  from 
3  cubic  inches  of  boiling  water  at  a  distance  of  400  yards  !  An 
analogous  difficulty — I  had  almost  said  impossibility — arises  in 
connection  with  the  question,  What  is  the  amount  of  light 
given  out  by  the  stars  ?  All  attempts  to  express  this  in  figures 
seem  to  me  perfectly  futile,  and  that  we  cannot  safely  do  more 
than  say  that,  contrasting  a  starless  night  with  a  night  on  which 
the  stars  are  shining  brightly,  there  is  in  the  latter  case  a 
sensation  of  less  darkness  than  in  the  former  case.  Beyond 
this  I  do  not  deem  it  safe  to  particularise. 

Fabry,  at  Marseilles,  published  in  1910  the  results  of  certain 
efforts  made  by  him  by  way  of  developing  previous  attempts  by 
Nevvcomb,  Burns,  and  Yntema,  a  Dutchman,  to  determine 
the  intrinsic  brightness  of  the  sky  so  far  as  star-light  was 


202  THE    STARS. 

concerned:  It  need  hardly  be  said  that  the  task  to  be  per- 
formed proved  a  very  difficult  one  and  the  results  very 
contradictory  all  round  ;  so  much  so  that  I  hesitate  to  attempt 
to  summarise  them,  beyond  saying,  what  is  an  evident 
truism,  that  the  stars  collectively  do  afford  some  light  to  the 
Earth. 

We  must  not  pass  away  from  the  consideration  of  the  stars 
as  isolated  or  single  objects  without  saying  something  on  the 
interesting  and  time-honoured  question  of  their  twinkling. 
This  optical  phenomenon  came  before  all  of  us  in  our  earliest 
years.  Who  has  forgotten  : — 

"Twinkle,  twinkle,  little  star; 
How  I  wonder  what  you  are  ! 
Up  above  the  world  so  high, 
Like  a  diamond  in  the  sky"? 

This  has  been  in  part  replaced  by  the  advance  of  modern 
science,  and  accordingly  we  have  the  following  revised  version 
in  circulation :  — 

"Twinkle,  twinkle,  little  star; 
Now  I've  found  out  what  you  are, 
When  unto  the  midnight  sky 
I  the  spectroscope  apply." 

Familiar  as  the  phenomenon  is  to  all  of  us,  full  scientific 
explanations  of  it  are  lacking.  In  its  effects  it  is  evidently 
largely  dependent  upon  the  condition  of  the  Earth's  atmosphere, 
the  varying  influence  of  which  undoubtedly  affects  the  extent 
of  the  twinkling  noticed  on  any  given  night.  The  weather 
indications  which  twinkling  bespeaks  seem  uncertain  when  it  is 
a  question  of  excessive  twinkling,  which  may  indicate  fine 
weather  or  the  approach  of  weather  of  the  contrary  character  ; 
but  it  seems  quite  certain  that  the  absence  of  twinkling  (that  is 
to  say,  if  the  stars  are  dull  and  devoid  of  rays)  renders  the 
approach  of  rain  a  certainty.  Bright  stars  twinkle  much  more 


TWINKLING    OF    THE    STARS.  203 

than  faint  ones  ;  indeed,  it  may  be  said  that  faint  stars  do  not 
twinkle  at  all.  Again,  stars  low  down  near  the  horizon  twinkle 
more  than  those  high  up  towards  the  zenith  ;  and  an  observer 
in  a  low-lying  position  on  the  Earth  will  notice  the  twinkling  to 
be  more  marked  than  when  he  looks  at  the  same  stars  from  a 
mountainous  or  considerably  elevated  level  above  the  sur- 
rounding country— in  other  words  sees  the  stars  through  a 
comparatively  rarefied  atmosphere.  These  facts  accentuate 
the  certainty  that  twinkling  is  a  matter  largely,  one  might 
perhaps  almost  say  wholly,  dependent  on  atmospheric  con- 
ditions. It  has  been  suggested,  however,  that  this  question  of 
the  density  or  rarefaction  of  the  air,  dependent  on  a  star's 
position  above  the  horizon,  must  not  be  pushed  too  far  because 
(as  is  supposed)  several  of  the  principal  fixed  stars,  presumably 
on  account  of  the  nature  and  peculiarity  of  their  light,  vary 
considerably  in  their  display  of  twinkling,  independently  of 
their  position  in  the  heavens.  For  instance,  Procyon  (a  Canis 
Minoris)  and  Arcturus  (a  Bootis)  twinkle  much  less,  under  all 
circumstances,  than  Vega  (a  Lyrae),  a  notable  bluish-white  star. 
A  French  observer,  Dufour,  has  laid  it  down  that  red  stars 
twinkle  less  than  white  ones  and  that  twinkling  is  more 
visible  during  twilight  than  later  on. 

The  subject  of  twinkling  was  very  exhaustively  studied  by  the 
late  C.  Montigny,  an  amateur,  who  lived  at  Brussels,  where 
I  had  many  interesting  conversations  with  him  in  188 — . 
He  arrived  at  some  very  striking  conclusions.  He  found 
that  twinkling  is  more  pronounced  when  rainy  weather  is 
impending,  and  also  more  pronounced  in  winter  than  in  summer. 
Dry  weather  in  spring  and  autumn  stands  on  about  the  same 
footing,  but  autumnal  wet  weather  developes  the  phenomenon 
in  a  much  more  marked  manner  than  does  spring  wet  weather. 
Variations  in  the  barometer  and  in  the  humidity  of  the  atmo- 
sphere, as  indicated  by  the  hygrometer,  also  affect  the  amount  of 
twinkling  ;  it  is  also  more  developed  when  a  rainy  period  likely 
to  last  two  or  three  days  is  approaching,  than  merely  before  a 


204  THE    STARS. 

single  casual  rainy  day  ;  it  also  varies  with  the  aggregate  total 
rainfall  of  a  group  of  days,  being  greater  as  the  rainfall  is 
greater,  suddenly  and  considerably  decreasing  directly  the  rain 
has  passed  away. 

Montigny's  observations  and  conclusions  were  not  based  on 
crude,  haphazard  eye-observations,  but  on  an  instrument  of  his 
own  invention,  which  he  called  a  scintilometer,  using  the  French 
word  for  twinkling  as  the  basis  of  the  name  of  his  appliance. 
He  found  the  number  of  scintillations  (angltcc,  twinkles) 
observable  per  second  to  vary  from  a  minimum  of  50  during 
June  to  July  to  97  in  January  and  101  in  February,  increasing 
or  decreasing  month  by  month  in  regular  gradation.  He  also 
found  that  a  display  of  Aurora  Borealis  exercised  a  marked 
influence  in  increasing  the  twinkling.  But  this  was  not  all  in 
regard  to  his  discoveries.  It  came  into  his  head  that  possibly 
the  different  classes  of  stars  as  classed  by  Secchi  with  respect 
to  their  spectra  might  yield  some  definite  results  in  regard  to 
twinkling;  and  he  was  not  disappointed.  Anticipating  here 
what  belongs  to  a  later  part  of  this  volume,  a  proper  account  of 
Secchi's  classes  of  stars,  I  may  state  that  Montigny,  as  the  result 
of  some  hundreds  of  observations  of  41  bright  stars  belonging 
to  Secchi's  first  3  classes,  was  led  to  the  following  conclu- 
sions :  that  stars  of  the  first  class  yielded  an  average  number  of 
86  scintillations  per  second,  stars  of  the  second  class  69,  and 
stars  of  the  third  class  only  56.  The  more  perfectly  any  star 
possesses  the  distinguishing  characteristics  of  its  class  the  more 
nearly  does  the  number  of  its  scintillations  agree  with  the  law 
indicated  by  the  above  statement.  This  law  may  be  stated  thus  : 
The  more  considerably  the  spectrum  of  a  star  is  interrupted 
by  dark  lines,  the  less  frequent  are  its  scintillations  ;  from 
which  it  follows  that  on  the  characteristic  of  each  star  depends 
its  twinkling,  both  as  regards  its  frequency  and  the  colours 
which  it  displays. 

Sufficient  has  now  been  said  by  way  of  treating  the  stars  as 
isolated  objects  in  the  heavens,  and  we  must  now  proceed  to 


DOUBLE    STARS. 


205 


consider  the  stars  in  combination,  beginning 
with  pairs  of  stars,  and  leading  up  to  clusters 
of  indescribable  multitudes.  I  pass  over  such 
recundite  matters  as  the  "  proper  motions  "  of 
stars,  "  star-drift,"  and  the  "  motion  of  the  Solar 
System  in  space,"  as  involving  difficult  technical 
details  not  likely  to  interest  the  readers  for 
whom  this  volume  is  primarily  intended. 


DOUBLE   STARS. 

A  very  large  number  of  stars,  including  some 
of  the  largest  and  some  of  the  smallest  visible, 
though  they  appear  to  the  naked  eye,  or  through 
an  opera-glass  or  a  small  telescope,  to  be  single 
stars,  yet,  with  increased  optical  assistance,  are 
found  to  consist  of  two  stars  so  close  together 
as  previously  to  have  been  regarded  as  only 
one  star.  Other  stars  seeming  to  be  single  are 
eventually  found  to  comprise  three  stars,  and  so 
on,  ifour  stars,  or  five  stars,  until  the  word 
"multiple"  has  to  be  used.  We  will  start 
with  a  common  form  of  double  star,  though  in 
numerous  cases  greatly  increased  optical  assist- 
ance shows  that  one  or  other  member  of  a  pair, 
regarded  only  as  a  pair,  is  itself  double  again. 
Up  to  the  time  of  Sir  W.  Herschel  very 
'few  double  stars  were  known.  His  powerful 
telescopes  enabled  him  to  convert  500  stars 
apparently  single  into  doubles  ;  and  now  the  re- 
searches and  perseverance  of  modern  observers 
have  resulted  in  the  number  of  recognised  double 
stars  being  increased  to  many  thousands. 

The   mere  fact  of  looking    at    a    star   and 
finding   it  in  a   small  telescope   to   be   single, 


Fig.  260.— 
Two  Stars 
at  Different 
Distances  seen 
as  a  "  Double 
Star." 


206  THE    STARS. 

whilst  a  larger  telescope,  or  more  power  on  the  small  one, 
reveals  its  duplicity,  though  a  thing  interesting  in  itself, 
falls  far  short  of  the  great  interest  which  attaches  to  many  of 
these  objects  after  prolonged  study  of  them.  Herschel  at 
first  merely  supposed  that  he  was  looking  at  2  stars  either 
stationary  side  by  side  at  the  same  distance  from  the  Earth 
or  at  2  stars  in  nearly  the  same  line  of  sight  at  distances 
altogether  different.  The  annexed  diagram  (Fig.  260)  will  make 
clear  what  is  involved  in  this  simple  statement  regarding  a  star 
only  optically  double.  Herschel,  however,  was  led  by  the  force 
of  circumstances  into  a  discovery  which  both  astonished  and 
captivated  him.  In  the  early  stages  of  his  work  as  a  double- 
star  observer  he  recorded  the  angular  position  of  all  his  double 
stars  with  respect  to  the  N.  and  S.  points  of  the  heavens,  and 
their  distances  from  one  another.  He  continued  observations  of 
this  character  for  the  sole  purpose  of  trying  to  discover  whether 
observations  at  different  periods  of  the  year  gave  indications 
of  his  stars  being  subject  to  displacement  by  way  of  parallax 
in  consequence  of  the  Earth's  annual  motion  round  the  Sun. 

Instead,  however,  of  obtaining  any  information  to  help  him 
as  regards  parallax,  he  found  in  a  very  large  number  of  cases 
that  these  pairs  of  stars  were  experiencing  relative  change,  and 
that  their  distances  were  varying  ;  as  also  the  angle  with  the 
meridian  of  a  line  joining  the  centres  of  the  2  stars.  In  other 
words,  he  found  that  there  were  in  existence  systems  consist- 
ing of  2  stars  revolving  about  each  other  in  elliptic  orbits, 
and  evidently  linked  together.  The  interest  attaching  to  this 
discovery  is  of  a  twofold  nature.  JjuirST'of  all,  there  was  the 
unforeseen  and  captivating  novelty  of  it,  and  then  there  was  the 
important  fact  that  it  was  ultimately  found  that  the  Newtonian 
Law  of  Gravitation  was  in  operation  far  beyond  the  confines  of 
the  solar  system  to  which  it  had  been  previously  supposed  to  be 
limited. 

The  actual  application  of  the  law  to  Herschel's  discoveries 
did  not  take  place  till  many  years  after  those  discoveries^  when 


PLOTTING    DOUBLE    STARS    MEASUREMENTS.  2C7 

Savary,  in  1830,  computed  an  orbit  for  the  star  £  Ursa  Majoris 
which  is  now  recognised  as  a  binary,  the  smaller  star  of 
which  steadily  circulates  round  the  larger  one  in  a  period  of 


Fig.  261.— Diagram  for  sketching  of  the  Corona  in  Total 
Eclipses  of  the  Sun. 

Devised  by  E.  J .  Stone,  and  available  for  plotting  measurements  of 
Double  Stars. 

about  60  years.  This  star  may  be  well  commended  to  the 
notice  of  amateurs  for  the  reason  that  both  components  are 
large,  the  larger  one  being  of  magnitude  4,  and  the  smaller  one 


208  THE   STARS. 

of  magnitude  5^,  and  the  distance  between  them  generally 
being  about  2"  of  arc,  more  or  less.  Herschel  made  his  dis- 
covery known  in  a  memorable  paper  presented  to  the  Royal 
Society  in  1802.  The  number  of  stars  which,  after  about  25 
years'  study,  he  found  to  be  endued  with  orbital  motion  was 
no  more  than  50,  but  since  his  day  an  immense  amount  of 
time  and  labour  has  been  bestowed  on  that  class  of  star,  and  the 
assured  binaries  are  now  to  be  numbered  by  hundreds,  not  to  say 
thousands,  if  we  takecount  of  those  which  are  suspectedof  motion. 

£  Ursa  Majoris  goes  through  its  changes  in  a  comparatively 
short  period  of  time— that  is  to  say,  there  are  not  many 
stars  whose  periods  are  shorter  than  60  years  ;  but  there 
are  a  great  number  whose  certain  periods  run  into  hundreds 
of  years,  and  therefore  with  many  of  them  prolonged  observa- 
tions, spread  over  a  long  expanse  of  years,  will  have  to  be 
carried  out  before  the  certainty  of  their  movements  and  the 
precise  details  thereof  can  be  established.  HerschePs  discoveries 
were  taken  up  and  turned  to  account  by  F.  G.  W.  Struve,  who 
in  1837  published  a  great  book  containing  measures  of  3112 
double  stars.  After  him  came  Dawes,  Secchi,  Seabroke,  and 
many  others  ;  but  the  greatest  living  observer  of  double  stars  is 
undoubtedly  the  American  astronomer  S.  W.  Burnham,  whose 
zeal  and  industry  have  attained  colossal  proportions,  but  he  has 
nowadays  many  fellow-labourers  in  various  parts  of  the  world. 
Burnham's  own  experiences  have  for  obvious  reasons  been 
somewhat  restricted  to  the  Northern  Hemisphere  with  some 
degrees  of  Southern  Declination  included  ;  but  a  great  develope- 
ment  of  double-star  work  is  now  proceeding  at  the  Cape  and  in 
Australia.  At  the  Cape  the  lead  is  being  taken  by  R.  T.  A. 
Innes,  the  Director  of  the  recently  established  Observatory  at 
Johannesburg,  in  the  Transvaal  ;  and,  as  time  goes  on,  we  may 
expect  a  large  output  of  work  from  that  centre. 

At  the  end  of  this  volume  a  list  will  be  given  of  some  of  the 
more  interesting  and  easy  double  stars  adapted  for  observation 
by  small  telescopes. 


FIG.  262 


PLATE  LXXXIV 


COLOURED     STARS. 

1.  i]  Cassiopeia?,  yellow  purple:     2.  7  Andromedae,  orange,  .areen ;     3.  «•  Piscium, 

pale  f^reen,  blue  :      4.   <•    Cancri,  orange,   blue  ;      5.  <*•    Circtni,  white,   brick  red  : 

6.  e  Bootis,  pale  orange,  pale  green. 


THE  COLOURS  OF  STARS.  209 

Many  double  stars  exhibit  the  curious  and  beautiful  pheno- 
menon of  complementary  colours.  In  such  cases  the  larger 
star  is  usually  more  or  less  reddish  or  orange,  and  the  smaller 
one  bluish-green  or  greenish-blue.  If  complementary  colours 
are  noticed  in  the  components  of  a  double  star  of  very  unequal 
size  the  circumstance  may  be  attributed  often  to  the  effect  of 
contrast.  Perhaps  it  may  be  useful  to  put  on  record  here  a 
table  of  the  complementary  colours,  though  somewhat  of  a 
digression,  for  the  subject  is  one  that  belongs  to  the  science  of 
optics  rather  than  to  astronomy  proper. 

Red  is  complementary  to  bluish-green. 
Orange         ,,.  ,,          sky-blue. 

Yellow         .,  ,,          violet-blue. 

Greenish-yellow        ,,          violet. 
Green  ,,  ,,          pink. 

The  meaning  of  the  foregoing  table  is  this  :  that  if  any  two 
colours  which  are  complementary,  as  above,  are  put  upon  a 
rapidly  revolving  disc  in  proper  proportions,  when  the  disc  is 
set  in  motion  on  its  axis  a  composite  tint,  almost  white,  is 
exhibited  to  the  spectator's  eye. 

As  regards  this  question  of  the  colours  of  double  stars,  an 
examination  made  many  years  ago  of  the  colours  assigned,  in 
Struve's  catalogue,  to  596  of  his  bright  stars,  yielded  the 
following  results  :  375  pairs  were  of  the  same  colour  and 
intensity  ;  101  pairs  were  of  the  same  colour  but  of  different 
intensity,  whilst  120  pairs  were  of  totally  different  colours. 

As  regards  the  colours  of  isolated  stars  not  treated  as 
doubles,  an  examination  of  the  heavens  will  lead  to  its  being 
noticed  that  single  stars  of  a  fiery  red  or  deep  orange  hue  are 
quite  common,  but  isolated  blue  or  green  stars  are  very  rare. 

In  looking  into  the  expressed  opinions  of  observers  who, 
under  various  circumstances,  have  made  statements  as  to  the 
colours  of  stars,  it  will  be  found  that  frequently  great  diversity 
exists — a  diversity  which  is  often  inexplicable,  and  which  it  is 


210  THE    STARS. 

hardly  permissible  to  put  down  to  actual  changes  of  colour. 
Subject  to  this  caution,  the  following  stars  may  be  named  as 
coloured  according  to  the  colours  prefixed  : — 

White  Stars. — a   Canis  Majoris,    a    Leonis,    /3    Leonis,   a    Lyrae, 

a  Piscis  Australis,  a  Ursas  Minoris. 
Red  Stars. —  a  Tauri.  a  Scorpii,  a  Orionis. 
Blue  Stars. — a   Aurigse,  ft  Orionis,  7  Orionis,  a  Canis  Minoris, 

a  Virginis. 

Green  Stars. — a  Aquike,  a  Cygni. 
Yellow  Stars.—*  Bootis. 

The  amateur  observer  will  find  it  interesting  to  compare  the 
statement  of  colours  just  given  with  his  own  ideas  on  the  subject 
as  obtained  by  naked-eye  observations ;  and  I  am  far  from 
saying  that  he  will  be  able  satisfactorily  to  confirm  the  accuracy 
of  the  statements  made  in  the  foregoing  table.  There  is  really 
only  one  thing  which  stands  out  conspicuously  certain  in 
regard  to  the  colours  of  stars,  and  that  is,  the  enormous  number 
which  are  dotted  all  over  the  heavens  which  exhibit  various 
shades  of  colour  intermediate  between  crimson  at  one  end  of 
the  scale  and  yellowish  at  the  other.  An  observer  who  sets 
himself  the  task  of  examining  this  matter  for  himself  will 
probably  be  surprised  at  the  immense  number  of  stars  to  which 
he  will  be  able  to  apply  the  word  "  orange "  (in  various 
gradations). 

Thus  far  we  have  been  considering  single  stars  and  pairs  of 
stars,  but  the  study  of  sidereal  astronomy  does  not  by  any 
means  end  here,  because,  when  examining  the  heavens,  we 
come  across,  as  already  indeed  mentioned,  triple,  quadruple, 
and  multiple  stars  ;  that  is  to  say,  stars  which  to  the  naked  eye 
appear  to  be  single,  but  which,  with  adequate  optical  assistance, 
are  found  to  be  compound,  as  these  various  designations  imply. 
It  is  not,  however,  necessary  to  dwell  on  these  stars,  except  for 
the  one  purpose  of  stating  that,  besides  there  being  pairs  of 
stars  which  we  call  "  binary,"  because  they  revolve  round  one 
another,  and  therefore  are  distinguishable  from  simple  optical 


PLATE  LXXXV 


COLOURED     STARS. 

7.  s  Bootis,   orange,   purple ;      8.  .t  Coronas,   white,   blue ;      9.  e  Normae,   bright 

green,    bright    purple;      10.  ct  Herculis,   orange,    emerald    green;      11.  ft  Cygni. 

yellow,  sapphire  blue  :     12.  ff  Cassiopeia?,  pale  green,  bright  blue. 


VARIABLE    STARS.  211 

double  stars,  which  are  only  double  in  appearance,  there  are 
certain  triple  stars  which  are  subject  to  the  complication  that 
there  are  three  stars  in  orbital  motion.  These  are  known  as 
"ternary"  systems.  Here  we  have  either  2  stars  revolving 
round  one  primary,  or  the  2  smaller  stars  of  the  trio  revolving 
round  one  another,  and  this  subordinate  pair  jointly  revolving 
round  the  3rd,  which  is  really  the  first,  and  needs  to  be  called 
the  primary  star  of  the  triple  system.  The  possible  complica- 
tions to  which  such  a  condition  of  things  brings  us  face  to  face 
are  very  obvious,  and  I  will  content  myself  by  inviting  the  reade/ 
to  inspect  the  diagrams  here  given  without  pursuing  the  matter 
into  further  detail. 

VARIABLE   STARS. 

Having  discussed  changes  of  colour  in  the  stars,  the  question 
of  changes  of  brightness  naturally  comes  next,  and  opens  up 
the  subject  which  bears  the  recognised  title  of  "  variable  stars." 
Suspicions  as  to  changes  in  the  brilliancy  of  particular  stars 
were  long  current,  but,  save  in  one  or  two  exceptional  instances, 
this  branch  of  sidereal  astronomy  is  of  modern  origin.  Seem- 
ingly, the  first  star  to  be  recognised  as  systematically  subject 
to  marked  changes  of  brilliancy  is  the  star  which  more  than 
2  centuries  ago  received  the  name  of  Mira  Ceti — a  phrase 
which  becomes,  when  duly  spread  out,  "  Mira  Stella,  the 
wonderful  star  in  the  constellation  Cetus,"  and  which  supporters 
of  new-fangled  pronunciation  try  to  indicate  by  calling  it  "  Meeray 
Say  tee"  !  Bayer  recorded  the  star  in  his  Atlas  of  1603,  and  gave 
it  the  designation  Omicron  (o),  and  this  is  still  its  accepted 
scientific  title. 

This  star  is  one  of  the  most  interesting  of  all  the  known 
variables,  alike  from  the  regularity  with  which  it  accomplishes 
its  changes  and  the  ease  with  which  those  changes  can  be 
observed  by  anybody.  Its  period  is  331  days  8  h.  ;  in  other 
words,  it  reaches  its  greatest  brightness  about  12  times  in 


212  THE   STARS. 

II  years,  when  it  sometimes  attains  the  brilliancy  of  a  star 
of  the  2nd  magnitude,  at  which  brilliancy  it  remains  stationary 
for  about  a  fortnight.  It  then  diminishes  during  about  3 
months,  until  it  sinks  down  to  a  star  of  magnitude  9^,  or  even 
becomes  totally  invisible.  It  remains  in  this  condition  for 
about  5  months,  and  then  gradually  recovers,  during  the 
next  following  3  months,  its  maximum  brilliancy.  The 
foregoing  periods  and  figures  are  only  to  be  regarded  as 
average  ones,  because  there  is  strong  evidence  that  the  changes 
of  this  star  are  themselves  subject  to  secondary  periods  of 
change  ;  that  is  to  say,  that  its  maximum  brilliancy  is  itself 
periodical,  and  that  every  eleventh  maximum  is  marked  by  a 
special  display  of  brilliancy  above  the  average.  Hence  it 
follows  that,  whilst  the  average  duration  of  the  naked-eye 
visibility  is  about  18  weeks,  in  1859-60  it  was  observed  with 
the  naked  eye  during  21  weeks,  whilst  in  1868  it  was  so  seen 
only  during  12  weeks.  The  variability  of  Mira  was  first  noticed 
in  1596  by  D.  Fabricius. 

Another  variable  star  of  great  interest,  perhaps  some  would 
think  almost  more  so  than  Mira  Ceti,  is  Algol  (/3  Persei),  the 
variability  of  which  stands  second  in  point  of  date,  for  it  seems 
to  have  been  first  recognised  by  Montanari  in  1669,  though  it 
was  not  until  observations  by  Goodricke  in  1782  that  its  period 
was  ascertained  with  some  degree  of  certainty.  This  is  gener- 
ally stated  in  the  following  form  :  The  normal  brightness  of  the 
star  is  that  of  mag.  2j.  From  this  it  descends  nearly,  but  not 
quite,  to  mag.  4  during  a  period  of  4h.  23m.  It  remains  at 
its  minimum  for  about  20 m.,  then  in  the  course  of  5h.  37111. 
it  regains  its  normal  maximum,  and  remains  there  for  about 
2d.  10  h.  The  time  occupied  in  the  entire  series  of  changes 
is  2d.  20  h.  48m.  The  further  study  which  has  been  given 
during  recent  years  to  the  subject  of  variable  stars  has  resulted 
in  the  discovery  of  a  not  inconsiderable  number  which  go 
through  their  changes  in  periods  measured  by  a  few  days,  and 
under  physical  circumstances  akin  to  those  which  govern  the 


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^  Uns^  MAJORIS. 


Fig.  266.  Fig.  267. 

Mean  Light-curves  of  certain  Variable  Stars. 


213 


214  THE   STARS. 

changes  of  Algol  ;  and  accordingly  we  now  speak  of  certain 
stars  as  "  stars  of  the  Algol  type  "  ;  and  by  way  of  explanation 
it  has  been  suggested  that  a  non-luminous  satellite  revolves 
round  the  primary  star  and  eclipses  it  at  stated  intervals. 

Another  variable  star  of  great  interest,  which,  like  Algol,  is 
very  handy  for  observers  in  the  Northern  Hemisphere,  is  8  Cephei, 
also  one  of  Goodricke's  stars,  and  recognised  by  him  in  1784 
to  be  a  variable.  Counting  from  minimum  to  minimum,  its 
period  is  5  d.  8h.  47m.,  and  its  range  of  brilliancy  from 
mag.  3!  to  mag.  4f,  or  thereabouts.  The  interval  between 
maximum  and  maximum  is  unequally  divided  as  regards  the 
minimum  stage,  for  the  time  occupied  in  descending  from 
maximum  to  minimum  is  considerably  greater  than  the  time 
occupied  in  rising  from  minimum  to  maximum.  The  intervals 
are  3d.  19 h.  and  id.  14 h.  respectively. 

,3  Lyrae  is  a  variable  which  differs  very  much  in  the  sequence 
of  its  changes  from  those  which  have  just  been  described,  for 
it  has  a  double  maximum  and  minimum  within  what  is  now 
recognised  to  be  its  complete  period  of  12  d.  21  h.  53m.  This 
peculiarity  misled  Goodricke,  who  discovered  the  variability 
of  this  star  in  1784,  and  induced  him  to  assign  to  it  a  period 
of  only  half  the  true  complete  period  as  just  given.  The 
changes  are  as  follows  :  starting  from  a  maximum  of  mag.  3^, 
the  star  descends  to  its  first  minimum  of  mag.  4 ;  then  it  rises 
to  maximum  again,  and  descends  to  a  second  minimum,  but 
at  this  second  minimum  it  descends  lower  than  before,  namely, 
to  mag.  4^.  It  is  easy  to  see  how  it  came  about  that  Good- 
ricke was  misled  into  fixing  the  period  at  one-half  its  true 
amount.  Argelander  ascertained  that  the  period  itself,  taken 
as  a  whole,  is  periodic  ;  that  up  to  1840  it  was  increasing,  and 
then  began  to  decrease,  which  decrease  was  still  in  progress 
when  he  made  that  remark  in  1866.  I  do  not  find  any  recent 
observations  which  throw  light  upon  this  point. 

The  foregoing  stars  all  belong  to  the  Northern  Hemisphere, 
but  the  Southern  Hemisphere  has  in  r)  Argus  a  once  naked- 


>OO  3OO  JOO 


T  URS^B  MAJORIS. 

<5^L 
Fig.  268. 


Fig.  270. 


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S  UKS^E  MAJORIS. 

/2  7    —     A3 

Fig.  289. 


R  CAM-ELOPARD     i 


Fig.  271. 


Mean  Light-curves  of  certain  Variable  Stars. 

215 


2l6  THE    STARS. 

eye  variable,  the  uncertainties  of  which  have  puzzled  several 
generations  of  astronomers.  Its  magnitude  during  the  past 
150  years  has  been  noted  as  4,  2,  i,  2,  i,  2^,  3,  4^,  5,  6,  7, 
7^.  This  last  magnitude  was  assigned  to  the  star  in  March 
1886,  and  since  then  rj  seems  to  have  further  gone  down  to 
mag.  8,  where  it  was  in  1907,  and  probably  is  still.  All  that 
we  can  infer  is  that  it  exhibits  two  or  three  maxima  at  intervals 
preparatory  to  a  great  descent  so  as  to  become  invisible  to 
the  naked  eye.  Schonfeld  summarily  settled  the  question  of 
period  by  saying  that  77  Argus  has  no  regular  period ;  and  there 
is  much  to  be  said  for  this  unsatisfactory  conclusion,  which 
accords  in  substance  with  the  opinion  of  Sir  J.  Herschel,  ex- 
pressed at  an  earlier  date,  that  this  is  a  star  "fitfully  variable 
to  an  astonishing  extent,  and  whose  fluctuations  are  spread 
over  centuries,  apparently  in  no  settled  period,  and  with  no 
regularity  of  progression." 

Thus  far  I  have  been  dealing  with  notable  naked-eye  stars, 
and  there  are  a  few  others  of  that  sort  which  can  hardly  be 
called  notable.  When,  however,  we  resort  to  the  telescope 
and  direct  our  attention  to  telescopic  variable  stars  an  enor- 
mous number  rush  in  upon  us,  many  of  them  of  great  interest 
to  those  who  possess  good  eyes,  patience,  and  telescopes  of 
adequate  power.  It  would  be  monotonous  and  somewhat 
beyond  the  scope  of  these  pages  to  particularise  any  of  these 
stars,  but  the  diagrams  here  given  will  convey  some  idea  of 
the  changes  which  they  undergo  and  the  delicate  character 
of  the  observations  required  before  safe  conclusions  can  be 
arrived  at. 

It  is  customary  with  astronomers,  when  they  wish  to  indicate 
in  the  most  easily  appreciated  form  variations  in  variable  stars, 
to  resort  to  diagrams  in  which  dates  and  magnitudes  are  repre- 
sented by  the  ordinates  and  abscissas  of  curves.  This  brings 
the  changes  much  more  readily  home  to  a  reader  than  mere 
tables  of  figures.  Figs.  264  to  275,  record  the  changes 
which  were  noted  to  have  taken  place  in  certain  well-known 


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Fig.  272. 


T  CEPHEJ. 
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Fig.  273. 


100  too 


S  CEPUEI. 


R  CASSIOPELE. 


Fig.  274.  Fig.  275. 

Mean  Light-curves  of  certain  Variable  Stars. 


217 


2l8  THE   STARS. 

variable  stars  at  the  dates  stated,  whilst  Fig.  276  records  the 
fluctuations  in  the  temporary  star  Nova  Persei  between 
February  and  April  1901  as  recorded  at  Oxford  by  Mr.  A.  A. 
Rambaut,  the  Radcliffe  observer. 

TEMPORARY   STARS. 

A  branch  of  sidereal  astronomy  which  has  much  of  the 
sensational  about  it  is  that  which  is  covered  by  the  title 
"Temporary  Stars."  At  many  epochs  in  the  world's  history 
there  have  suddenly  burst  forth  in  the  heavens,  and  shone  as 
bright  stars  for  limited  periods  of  time,  stars  which  probably 
ought  not  to  be  called  stars  at  all.  Some  of  the  objects  thus 
recorded  by  old  monastic  and  other  writers  undoubtedly  were 
only  mere  luminous  meteors,  or  fireballs,  and  a  few  of  them 
comets  ;  but,  apart  from  these  objects  we  have  trustworthy 
records  of  stars  suddenly  becoming  visible  in  places  where  no 
stars  had  been  seen  before,  and  which  remained  visible  for 
weeks  or  months  before  their  final  disappearance.  The  cases 
are  not  numerous  of  a  star  suddenly  appearing  and  rising  in 
brilliancy  to  become  conspicuous,  for  it  has  been  more  common 
for  a  conspicuous  star  to  appear  suddenly  in  a  place  where  no 
star  had  been  previously  seen,  and  then  at  once  to  begin  a 
downward  career. 

It  will  be  prudent,  if  we  desire  to  take  our  stand  on  the  firm 
ground  of  fact,  not  to  go  too  far  back  in  seeking  for  instances 
of  temporary  stars,  and  Tycho  Brahe's  star  of  1572  in  Cassio- 
peia is  the  most  ancient  which  I  desire  to  put  forward.  He 
has  left  us  a  full  account  of  it,  the  substance  of  which  is  that 
it  became  visible  in  November  1572,  and  remained  visible 
for  17  months,  or  till  March  1574.  At  its  best  it  was 
brighter  than  Sirius,  and  rivalled  Venus.  Tycho  Brahe,  having 
no  telescope,  of  course  lost  the  star  as  soon  as  it  descended 
below  the  6th  magnitude,  and  nobody  seems  to  have  seriously 
attempted  to  look  into  the  matter  until  D'Arrest,  in  1864,  pub- 


TEMPORARY    STARS. 


2I9 


lished  a  map  of  an  area  in  Cassiopeia  which  was  supposed  to 
include  the  place  of  Tycho's  star.  Argelander,  having  assigned 
a  position  to  the  star,  pointed  out  that  there  was  a  little  star 
almost  exactly  in  the  right  place,  and  Hind  and  Plummer 
followed  this  up  in  1873  by  stating  that  this  little  star  was 
variable.  There  the  matter  remains,  no  one  apparently  having 
attempted  to  follow  it  up  since.  The  exact  position  of  Tycho's 


Fig.  276.— Light  Changes  in  Nova  Persei,  1901. 

star,  as  given   by  Argelander,  brought  up   for  precession  to 
January  i,  1913,  is  as  follows  : — 


R.A. 


h.  m.    s. 
O   19  56 


Declination     .     63°  40-0'  N. 


The  reason  that  some  attention  was  given  to  the  subject  in 
1873  was  tnat  tne  theory  was  current  that  Tycho's  star  was  a 


220  THE    STARS. 

reappearance  of  objects  alleged  to  have  been  temporary  stars, 
and  visible  in  945  and  1264  ;  so  that,  if  those  objects  had  been 
temporary  stars,  there  was  the  slight  possibility  (very  slight) 
that  Tycho's  star  was  the  reappearance  of  a  variable  star  whose 
period  was  300  years,  more  or  less.  But  all  this  would  seem  to 
be  an  argument  devoid  of  foundation,  and  there  is  no  solid 
reason  whatever  for  suspecting  that  Tycho's  star  was  to  reappear 
after  the  lapse  of  three  centuries. 

The  year  1604  was  marked  by  the  appearance  of  a  temporary 
star  in  the  constellation  Ophiuchus,  which  became  nearly  as 
bright  as  Venus,  and  lasted  a  year  or  more.  Kepler  wrote  a 
book  about  it  which  has  come  down  to  us. 

In  1670  a  new  star  appeared  in  Cygnus,  which  rose  to  the 
brightness  of  a  star  of  the  3rd  magnitude,  and  lasted  two  years 
from  first  to  last,  during  which  period  it  more  than  once 
increased  in  brightness,  and  then  diminished,  before  it  finally 
disappeared. 

A  long  interval  elapsed  before  we  had  another  new  star. 
On  April  28,  1848,  a  5th-magnitude  star  was  seen  by  Hind  in 
Ophiuchus,  which  a  few  weeks  later  rose  to  the  4th  magnitude, 
and  then  descended  to  the  nth  or  I2th  magnitude,  at  which  it 
may  or  may  not  still  be. 

May  1866  gave  us  a  new  star,  which  created  a  considerable 
sensation  because  of  the  sudden  outburst  which  characterised 
it.  As  a  star  of  mag.  9^  it  was  recorded  by  Argelander 
in  1855,  but  Birmingham,  at  Tuam,  in  Ireland,  saw  it  on 
May  12,  1866,  as  a  star  of  mag.  2.  Combining  the  negative 
testimony  of  Schmidt,  of  Athens,  with  the  positive  testimony 
of  Birmingham,  it  would  seem  that  this  star  suddenly  rose 
from  the  4th  to  the  2nd  magnitude  in  about  three  hours 
on  the  evening  on  which  Birmingham  saw  it.  It  soon  began 
to  fade  away,  and  by  the  end  of  the  month  had  fallen  to 
mag.  8.  It  continued  below  magnitude  9  all  through  the 
following  summer,  but  rose  to  7^  in  September,  and  was 
nearly  stationary  in  brightness  for  the  remainder  of  the  year. 


QVADRANS  MVRAL1S  SIVE  TICHONICUS. 


Fig.  277.— Tycho  Brahe's  Mural  Quadrant  for  measuring 
Vertical  Angles. 


222  THE    STARS. 

This  star  is  now  permanently  put  upon  the  list  of  variable 
stars  under  the  designation  of  T  Coronae  ;  but  it  seems  to 
have  been  ignored  by  variable-star  observers  during  recent 
years. 

On  November  24,  1876,  Schmidt,  at  Athens,  observed  anew 
star  of  the  3rd  magnitude  in  Cygnus,  yellowish  in  colour.  By 
the  end  of  December  it  had  descended  to  the  7th  magnitude, 
and  afterwards  became  still  "smaller.  The  last  recorded 
observation  of  it  which  I  have  been  able  to  find  is  dated 
September  2,  1877,  when  the  spectrum  was  reduced  to  a  single 
line,  the  continuous  spectrum  and  all  the  other  lines  having 
disappeared. 

August  1885  saw  the  outburst  in  the  constellation  Andromeda 
of  a  new  star,  which  created  at  the  time  a  great  deal  of  excite- 
ment. This  excitement  was  largely  due  to  the  position  of  the 
star,  which,  seemingly  in  the  great  nebula,  was  not  of  it,  having 
the  appearance  of  standing  out  sensibly  in  front  of  the  nebula. 
When  first  seen,  which  appears  to  have  been  on  August  22,  or 
a  few  days  previously,  the  star  was  of  about  the  6th  magnitude. 
It  never  got  beyond  that,  and  rapidly  began  to  decline  until  it 
reached  about  the  iith  magnitude,  and  then  it  became  visually 
lost  in  the  nebula,  though  from  first  to  last  the  impression 
conveyed  on  those  who  viewed  it,  including  myself,  was  that 
it  had  nothing  to  do  with  the  nebula  itself. 

Later  in  the  same  year,  on  December  17,  J.  E.  Gore  found 
a  new  star  in  Orion  which,  during  its  visibility,  passed  from 
mag.  6  to  mag.  9,  or  less,  and  then  disappeared,  and 
afterwards  again  came  into  view,  and  is  now  permanently 
enrolled  as  a  variable  star,  though  no  explanation  can  be  offered 
of  its  sudden  increase  of  light  in  the  month  in  which  it  was 
first  found.  It  is  now  known  as  U  Orionis. 

Early  in  1892  a  new  star  appeared  in  the  constellation 
Auriga,  the  circumstances  connected  with  which  are  highly 
interesting.  The  fact  of  the  star's  existence  was  communicated 
to  Dr.  Copeland,  Director  of  the  Observatory  of  Edinburgh, 


NEW    STARS.  223 

by  means  of  an  anonymous  postcard,  which  led  him  at  once 
to  search  for  and  find  the  star,  which  he  was  told  was  of  the 
5th  magnitude.  The  authorship  of  the  postcard  was  after- 
wards avowed  by  a  certain  Dr.  Anderson,  who  found  the  star 
by  means  of  McClure's  edition  of  Klein's  Star  Atlas,  used  in 
conjunction  with  a  small  pocket-telescope. 

When  news  of  the  discovery  was  conveyed  to  the  other  side 
of  the  Atlantic,  Professor  Pickering,  of  Harvard  College 
Observatory,  found  that  Anderson's  star  had  been  photo- 
graphed by  him  13  times  between  December  10,  1891,  and 
January  20,  1892.  He  considered  that  his  plates  took  all  stars 
down  to  the  9th  magnitude,  and  that,  as  the  new  star  did  not 
appear  on  the  plate  of  December  8,  it  must  have  brightened 
up  between  December  8  and  December  10.  The  new  star, 
henceforth  known  as  Nova  Aurigas,  remained  of  the  4th  or  5th 
magnitude  till  the  end  of  February,  when  it  rapidly  diminished, 
and  on  April  26  was  no  more  than  of  the  i6th  magnitude. 
Later  on  in  the  summer  it  brightened  up  to  about  the  loth 
magnitude,  and  then  fell  again  to  the  I2th  magnitude. 

In  1901  a  new  star  appeared  in  Perseus,  which  lasted  a  long 
time,  and  underwent  various  and  noteworthy  changes.  There 
is  some  little  uncertainty  as  to  who  first  discovered  it.  It 
seems  to  have  had  several  independent  discoverers  on  Febru- 
ary 22,  but  the  first  public  announcement  was  made  by 
Dr.  Anderson  of  Edinburgh,  the  discoverer  of  Nova  Aurigce 
nine  years  previously.  It  is  interesting  to  add  that  it  was  also 
discovered  on  the  same  night,  February  21,  at  KiefT,  in 
Russia,  by  a  boy  16  years  of  age  named  Borisiak.  When 
Dr.  Anderson  first  saw  the  star  he  put  its  magnitude  at  2|, 
whilst  Borisiak,  perhaps  erroneously,  called  it  i£.  The  evidence 
as  to  its  history  seems  to  show  that  on  February  20  the  star 
had  not  become  visible.  After  February  22  it  became  a  very 
bright  ist-magnitude  star,  though  it  only  remained  such  for  a 
day  or  two,  and  by  March  18  had  descended  to  the  4th  magni- 
tude, which  in  June  had  become  the  6th  magnitude,  and  at  the 


224  THE   STARS. 

end  of  the  year  the  yth.  These  changes  were  not  regular, 
because  its  brilliancy  oscillated  several  times.  The  final  history 
of  this  Nova  was  very  remarkable,  because  it  seems  to  have 
either  turned  into  a  nebula,  or,  in  some  mysterious  way,  to 
have  given  birth  to  one  ;  but  the  details  as  to  this  would  occupy 
too  much  space  for  these  pages. 

Other  new  stars  of  recent  date  are  the  following  :  Nova 
Lacertae,  discovered  on  December  30,  1910,  by  the  Rev. 
T.  E.  Espin  ;  Nova  Sagittarii,  discovered  photographically  in 
September  1899  at  Arequipa,  in  Peru,  but  the  fact  not  known 
till  an  examination  of  the  plates  in  1911  ;  Nova  Geminorum, 
discovered  in  March,  1912,  by  Enebo  at  Dombaas,  in  Nor- 
way. It  showed  spectroscopically  the  characteristic  hydrogen 
bands,  accompanied  by  dark  bands  on  the  side  towards  the 
violet. 

Professor  E.  C.  Pickering,  in  1881,  proposed  the  following 
classification  to  link  together  all  the  stars  which  come  under 
the  designation  of  "  temporary  "  or  "  variable  "  stars  : 

1.  Temporary  stars.     Examples  :  Tycho  Brahe's  star  of  1572, 
new  star  in  Corona  1866. 

2.  Stars  undergoing  great  variations  in  light  in  periods  of 
several  months  or  years.     Examples  :  o  Ceti,  and  x  Cygni. 

3.  Stars  undergoing  slight  changes  according  to  laws  as  yet 
unknown.     Examples  :  a  Orionis  and  a  Cassiopeia?. 

4.  Stars  whose  light  is  continually  varying,  but  the  changes 
repeated  with  great  regularity  in  a  period  not  exceeding  a  few 
days.     Examples  :  /3  Lyrse  and  8  Cephei. 

5.  Stars  which  every  few  days  undergo  for  a  few  hours  a 
remarkable  diminution  in  light,  this  phenomenon  recurring  with 
great  regularity.     Examples  :  j3  Persei  and  S  Caneri. 

In  the  case  of  stars  belonging  to  class  5,  the  observed 
variations  could  be  very  satisfactorily  explained  by  the  theory 
that  the  reduction  in  light  is  caused  by  a  dark  eclipsing 
satellite. 

The  foregoing  accounts  of  recent  new  stars  will  suffice   to 


OPENINGS    FOR    WORK.  225 

give  the  reader  a  general  idea  of  what  these  objects  are,  and 
I  hope  to  bring  it  home  to  amateur  astronomers  that,  if  they 
choose  to  avail  themselves  of  opportunities  which  from  time  to 
time  occur,  they  may  often  be  able  to  render  useful  service  to 
science,  and,  at  the  same  time,  to  earn  some  credit  and  distinc- 
tion for  themselves. 


CHAPTER    XII. 
GROUPS   OF   STARS   AND   NEBULA 

Stars  in  groups  classified. — Irregular  groups. — Clusters  of  stars  more 
or  less  compressed. — Nebula. — Classification  of  nebula. — Annular 
nebula. — Elliptic  nebula. — Spiral  nebula. — Planetary  nebula. — 
Nebulous  stars. — Large  nebula  of  irregular  form.— Exemplification 
of  these  classes  named. — Distribution  of  nebula  and  clusters  over 
the  heavens. — The  Milky  Way. — Brief  description  of  its  position. — 
Its  historic  names. 

HAVING  started  in  the  previous  chapter  with  single  stars  and 
gradually  got  up  to  multiple  stars — which  phrase  may  be  said  to 
mean,  say,  half  a  dozen  stars  under  one  roof,  as  it  were — we 
must  now  pass  on  to  groups  of  stars  which  are  to  be  met  with 
in  the  heavens  in  great  numbers  and  embracing  all  gradations 
of  quantity  from  a  few  dozen  up  to  literally  myriads,  according 
to  the  Greek  use  of  that  word.1 

The  variety  of  these  groups  to  be  found  in  the  heavens  is 
very  great,  both  as  regards  the  number  of  the  stars  composing 
the  groups,  and  also  as  to  their  general  shape.  We  may  con- 
veniently consider  the  objects  now  to  be  described  under 
three  general  heads,  the  third  of  which  will  need  special 
subdivision  by  itself.  The  three  main  divisions  may  be  as 
follows  :— 

(1)  Irregular  groups,  many  of  them  visible  to  the  naked  eye. 

(2)  Clusters   of  stars   more    or  less   compressed  and   sym- 

1  /xupiot  =  ten  thousand,  also  "countless." 
226 


FIG.  278 


PLATE  LXXXVI. 


The  Pleiades  (Tempel). 

With  the  Nebula  near  Merope. 


226] 


FIG.  279 


PLATE   LXXXVII. 


Nebulae  in  the  Pleiades,  Dec.  8,  1888  ( Isaac  Roberts). 


[227 


CLASSIFICATION    OF    CLUSTERS    AND    NEBUL/E.          227 

metrical,   and   resolvable   into    separate    stars   with    adequate 
optical  assistance. 

(3)  Nebulae  for  the  most  part  irresolvable,  however  powerful 
may  be  the  telescopes  which  are  brought  to  bear  on  them. 

The  third   class   may  be   subdivided    as    follows,   the   sub- 
divisions having  regard  chiefly  to  differences  of  shape. 
(i)  Annular  nebulas. 

(ii)  Elliptic  nebulas. 

(iii)  Spiral  nebulas. 

(iv)  Planetary  nebulae. 

(v)  Nebulous  stars. 

(vi)  Large  nebulas  of  irregular  form. 

The  foregoing  classification  may  be  considered  as  compre- 
hending all  the  known  clusters  and  nebulas  ;  but  the  reader 
must  be  warned  beforehand  that  only  a  few  objects  in  some  of 
the  classes,  and  none  in  the  other  classes  are  at  all  within  the 
reach  of  the  comparatively  small  telescopes  which  the  readers 
of  this  work  are  supposed  to  possess. 

Many  of  the  objects  in  class  (i)  are  more  or  less  non-teles- 
copic, so  to  speak  ;  that  is  to  say,  are  too  large  and  scattered 
to  be  advantageously  viewed  in  any  telescope  other  than  a  low- 
power  opera-glass  with  a  very  large  field. 

The  Pleiades  and  Hyades,  both  in  Taurus,  are  undoubtedly 
the  best  known  of  these  groups.  Indeed,  so  old  are  they 
historically  that  the  first  mention  of  them  begins  with  Homer. 
The  tradition  is  well  known,  and  as  old  as  Ovid,  that  there 
were  originally  7,  but  that  one  of  them  has  been  lost.  The 
origin  of  this  idea  is  unknown,  and  it  would  seem  that  one 
ought  to  say  that  the  tradition  is  scientifically  untrue,  because, 
not  only  can  7  still  be  counted,  but  a  good  many  more. 
This  group  is  really  a  very  good  test  of  eye-sight,  because, 
whilst  ordinary  eyes  often  do  not  get  beyond  six  in  the 
counting,  good  eyes  and  extra  good  eyes  can  get  up  to  8,  10, 
or  even  12.  A  proof  that  there  is  nothing  magical  in  the 
number  7  is  found  in  the  fact  that  9  of  the  stars  have  for 


228  GROUPS    OF    STARS    AND    NEBULA. 

unnumbered  centuries  borne  specific  names,  which,  with  their 
magnitudes,  are  as  follows  :  The  brightest  is  known  as  Alcyone 
(alias  r)  Tauri)  of  the  3rd  magnitude  ;  next  come  Electra  and 
Atlas,  both  3^  ;  then  Maia  4,  Merope  4^,  Taygeta  4^,  whilst 
Celeno,  Asterope,  and  Pleione  are  all  much  about  the  same 
size,  say  mag.  6.  But  besides  these  more  or  less  conspicuous 
members  of  the  group,  several  dozen  stars  of  smaller  size  are 
revealed  in  the  telescope.  There  is  a  matter  connected  with 
the  Pleiades  which  is  somewhat  mysterious.  In  1859  a  well- 
known  observer,  Tempel,  noticed  amongst  the  group  an  object 
which  he  took  to  be  a  telescopic  comet ;  but,  as  it  was  after- 
wards found  to  be  a  fixture,  and  not  to  be  moving,  it  was  clear 
that  it  was  not  a  comet,  but  a  nebula  which  had  suddenly 
manifested  itself.  As  time  went  on  and  attention  was  given  to 
the  subject  it  became  certain,  not  only  that  Tempel  had 
observed  a  genuine  nebula,  but  that  nebulous  matter  was  to 
be  seen  in  various  parts  of  the  cluster,  no  less  than  five  of 
the  chief  stars  (Alcyone,  Electra,  Maia,  Merope,  and  Celeno) 
being  involved  in  nebulosity.  It  seems  certain  that  this 
nebulous  matter  has  only  come  into  view  during  the  past 
half-century,  but  it  is  impossible  to  offer  any  explanation  of 
the  fact. 

The  Hindoos  call  the  Pleiades  "The  Hen  and  Chickens." 
The  Australian  black-fellows  call  them  "  Meamei  "  =  "  The 
Seven  Sisters."  In  Don  Quixote  Sancho  Panza  describes  his 
fancied  ride  through  space,  saying  :  "  We  happened  to  travel 
that  road  where  the  seven  she-goat  stars  were  "  ;  and  the  Don 
adds  :  "  It  was  impossible  for  us  to  reach  that  part  where  are 
the  Pleiades,  or  the  seven  goats,  as  Sancho  calls  them." 

The  Hyades  constitute  a  group  of  stars  altogether  inferior  to 
the  Pleiades  in  interest,  not  only  because  the  stars  are  smaller, 
but  because  they  are  much  scattered.  Still,  they  must  be 
treated  as  being  a  group,  and  they  have  been  recognised  as  such 
for  many  centuries. 

In  the  constellation  Cancer  we  have  another  historic  group 


FIG.  280 


PLATE   LXXXV1II. 


The  Cluster  13  M.  Herculis  (W.  E.  Wilson}. 


2281 


FIG.  281 


PLATE    LXXXIX. 


[229 


CONSPICUOUS    CLUSTERS  229 

known  as  Praesepe,  which  makes  a  very  effective  show  in  a 
telescope  of  large  field  and  low  power.  This  object  is  some- 
times met  with  in  old  scientific  books  under  the  name  of  the 
"  Bee-hive,';  but  that  name,  as  well  as  its  Latin  name,  is  lost  in 
antiquity.  Fully  2000  years  ago  it  was  recorded  by  two  Greek 
authors  as  available  to  indicate  the  approach  of  rain,  the  idea 
being  that,  under  such  prospect,  the  group  lost  its  sharp  stellar 
appearance  and  became  misty. 

The  constellation  known  as  Coma  Berenices  is  made  up  of 
a  number  of  stars  which,  though  it  may  be  named  in  connec- 
tion with  the  three  preceding  groups,  has  its  constituent 
stars  too  scattered  to  be  quite  fairly  comparable  with  them. 

We  must  now  proceed  to  consider  the  objects  which  are 
included  under  the  second  of  the  main  heads  already  specified, 
namely,  Clusters  of  Stars.  These  are  of  various  sizes  and 
shapes.  Many  of  them  appear  in  small  telescopes  as  nebulas 
and  nothing  else,  but  in  some  cases  even  a  small  amount  of 
additional  optical  power  renders  it  easy  to  see  that  the 
seemingly  nebulous  mass  really  consists  of  a  number  of 
separate  stars.  A  certain  number  of  the  objects  belonging 
to  the  class  which  we  are  now  considering  are  specially  labelled 
"  Globular  Clusters."  They  have  received  this  name  because 
they  present  the  appearance  of  stars  massed  together  as  globes, 
though  the  causes  which  gave  them  this  form  and  keep  them 
retaining  it  are  unknown.  The  most  striking  object  of  this 
character  in  the  Northern  Hemisphere  is  the  cluster  known  as 
13  M.  Herculis  for  which  the  Southern  Hemisphere  provides 
a  magnificent  counterpart  in  the  clusters  surrounding  the  Stars 
co  Centauri  and  47  Toucani. 

The  letter  M.  attached  to  the  cluster  in  Hercules,  just  named, 
deserves  explanation.  It  stands  for  the  initial  of  the  surname 
of  a  famous  French  astronomer,  Messier,  who  earned  the 
thanks  of  posterity  by  cataloguing,  nearly  a  century  and  a  half 
ago,  all  the  objects  in  the  heavens  which  he  was  able  to 
observe  in  a  telescope  with  an  aperture  of  only  2  inches. 


230  GROUPS    OF    STARS    AND    NEBULAE. 

With  such  a  telescope  he  was  naturally  unable  to  realise  very 
distinctly  the  difference  between  the  objects  which  we  now 
call  clusters  and  those  which  we  call  nebulae  ;  and  he  lumped 
all  together  under  the  comprehensive  title  "  Nebulosities  and 
Masses  of  Stars."  His  labours,  notwithstanding  that  his 
opportunities  were  limited,  are  still  of  use  to  us  in  so  far 
that,  whenever  we  come  across  a  cluster  or  nebula  with 
Messier's  number  and  letter  prefixed  to  it,  we  know  at  once 
that  it  can  be  seen  with  a  small  telescope,  however  imperfectly. 

Smyth  described  13  M.  Herculis  as  "an  extensive  and  mag- 
nificent mass."  Sir  J.  Herschel  saw  signs  of  its  stars  forming 
curved  lines,  which  feature  Lord  Rosse  interpreted  as  indicating 
a  spiral  formation.  I  have  not  myself  seen  o>  Centauri  or 
47  Toucani,  and  therefore  cannot  speak  of  them  from  personal 
knowledge  ;  but,  judging  by  the  language  used  by  those  who 
have  seen  them,  they  must  be  magnificent  objects,  surpassing 
the  cluster  in  Hercules.  Indeed,  Pickering  expressly  describes 
<»  Centauri  as  "  undoubtedly  the  finest  in  the  sky,"  and  47 
Toucani  as  "  second  only  "  to  w  Centauri. 

Next  to  this  as  regards  the  clusters  visible  in  England  seems 
to  come  5  M.  Libras,  very  accurately  described  by  Webb  as  a 
"beautiful  assemblage  of  minute  stars  greatly  compressed  in 
the  centre."  Sir  W.  Herschel  counted  not  less  than  200  stars 
in  it,  whilst  Smyth's  description  is  very  accurate  in  saying  that 
it  has  "  out-liers  in  all  directions  and  a  bright  central  blaze." 
Messier  committed  himself  to  an  opinion  respecting  this  cluster 
which  illustrates  a  remark  which  I  have  already  made,  that 
these  objects  vary  much  in  appearance,  according  to  the  size  of 
the  telescope  employed  in  viewing  them.  We  shall  see 
presently  many  proofs  of  this.  Meanwhile,  Messier's  remark 
respecting  5  M.  Librae  should  be  posted  up  as  a  caution  to  men 
of  science.  "  He  assured  himself  that  it  did  not  contain  a 
single  star." 

Other  clusters  of  the  type  of  those  which  have  gone  before 
will  be  found  amongst  the  list  in  the  Appendix. 


FIG.  282 


PLATE   XC. 


FIGS.  283-285 


PLATE   XCI. 


2  M.  Aquarii.  5  M.  Librae. 

(Sir  J.  Herschel.) 


2  M.  Aquarii  (Earl  of  Rosse). 

This  picture  shows  how  a  large  telescope  opens  out  the  stars  which 

[appear  squeezed  together  in  a  small  telescope.  [231 


REMARKABLE    CLUSTERS.  23! 

Respecting  one  of  these  globular  clusters,  80  M.  Scorpii,  a 
singular  circumstance  is  on  record.  In  1860  a  well-known 
observer  Pogson,  directing  his  telescope  to  a  part  of  the 
heavens  which  should  have  included  the  cluster,  found  that  it 
had  disappeared,  and  that  a  7th-magnitude  star  was  occupying 
its  place.  A  fortnight  later  the  star  had  disappeared  and  the 
cluster  was  again  visible,  presenting  its  normal  appearance. 
These  changes  were  also  noticed  by  two  German  observers, 
and  therefore  there  can  be  no  doubt  about  their  reality.  It 
seems  impossible  to  suppose  that  any  physical  change  had 
taken  place  in  the  cluster,  and  the  conclusion  is  therefore 
inevitable  that  the  star  was  a  temporary  one,  quite  independent 
of  the  cluster,  which  had  burst  out  in  front  of  it  and  lasted  a 
very  few  days,  and  had  then  disappeared,  owing  to  the  operation 
of  some  unknown  cause  or  causes. 

Of  clusters,  not  globular,  but  large  and  attractive,  67 
M.  Cancri  may  be  named  as  noteworthy.  But  by  far  the 
most  striking  and  beautiful  of  the  loose  and  irregular  clusters 
in  the  heavens,  probably  that  which  surrounds  the  star  K.  Crucis 
is  the  finest.  Sir  J.  Herschel,  when  at  the  Cape  in  1833  and 
following  .years,  observed  this  cluster  and  described.it  as 
one  of  the  most  beautiful  of  its  class.  Some  40  years  later, 
Russell,  at  the  Sydney  Observatory,  carefully  charted  its  stars, 
with  the  result  that  he  found  that  many  of  them  in  the  40 
years'  interval  had  moved  from  Herschel's  position,  and  in 
consequence  (it  was  to  be  assumed)  of  their  being  endued 
with  proper  motion.  Russell's  description  of  the  cluster  is  as 
follows:  "The  colours  of  this  cluster  are  very  beautiful,  and 
fully  justify  Herschel's  remark  that  it  looks  like  a  '  superb  piece 
of  fancy  jewellery.'  " 

We  will  now  pass  on  to  the  nebulae,  properly  so-called,  the 
number  of  which  has  been  greatly  augmented  of  recent  years. 
Sir  W.  Herschel  developed  Messier's  catalogue  of  103  objects 
into  hundreds,  which  Sir  John  Herschel's  labours  at  the  Cape 
and  elsewhere  brought  up  to  thousands.  In  1864  he  published 


232  GROUPS    OF    STARS    AND    NEBUL/E. 

a  complete  general  catalogue  of  all  those  then  known,  which 
numbered  5079  objects.  This  catalogue  seems  to  have 
stimulated  the  developement  of  this  branch  of  sidereal  astro- 
nomy, because  when  Dreyer  republished  Sir  John  Herschel's 
catalogue  revised,  corrected  and  enlarged,  the  new  edition 
comprised  7840  objects  ;  and  this  number  has  since  been 
largely  added  to,  especially  by  work  in  America,  and  as  the 
incidental  res.ult  of  searches  for  new  comets  and  double  stars.1 

It  should  be  clearly  stated  that,  for  the  profitable  examination 
of  nebulas  of  all  kinds,  large  telescopes  are  indispensable,  and 
that  the  number  which  can  be  viewed  even  with  moderate 
satisfaction  in  small  ones  is  very  limited  ;  but,  in  order  to 
present  a  complete  survey  of  these  objects,  according  to  the 
classification  laid  down  on  a  previous  page,  I  shall  be  obliged 
to  name  a  certain  number  which  are  hopelessly  beyond  the 
reach  of  small  telescopes. 

Of  "Annular  Nebulae  "  the  heavens  afford  only  a  few  examples 
— scarcely  a  dozen  in  all.  The  most  remarkable  is  57  M.  Lyras, 
situated  about  midway  between  /3  and  y  Lyras,  and  the  only 
annular  nebula  within  reach  of  a  telescope  of  moderate  power. 
Sir  J.  Herschel  described  this  as  having  the  appearance  of  a 
flat,  oval,  solid  ring  with  the  central  vacuity  not  quite  dark, 
out  "  filled  in  with  faint  nebula  like  a  gauze  stretched  over  a 
hoop."  Lord  Rosse,  Chacornac,  and  Secchi,  all  claimed  to 
have  resolved  this  object  into  stars,  whilst  Huggins  asserted 
that  it  was  wholly  gaseous. 

This  question  of  gaseous  nebulae  seems  to  'me  one  of  great 
difficulty  in  several  respects,  and  I  must  confess  myself  not  to 
be  satisfied  with  many  of  the  claims  put  forward  based  on 
spectroscopic  observations. 

"  Elliptic  Nebulae  "  of  various  degrees  of  eccentricity  are  not 
uncommon,  but  there  is  only  one  conspicuous  large  one,  namely, 

1  If  I  do  not  make  use  anywhere  of  the  phrase  "  white  nebulae,"  which  some 
writers  have  recently  tried  to  acclimatise,  it  is  because  I  think  it  an  unneces- 
sary and  illogical  phrase.  Practically  all  nebulae  are  "  white." 


PLATE    XCII. 


The  Clusters  33  and  34  Ijl  VI.  Persei  (A.  A.  Rambaut,  Radcliffe 

Observatory,  Oxford}. 


232] 


PLATE    XC1II. 


The  Great  Nebula  in  Andromeda  (H.  J.  Shepstowe). 


[232.1 


FIGS.  288-289 


PLATE    XCIV. 


FIG.  290 


PLATE    XCV. 


Spiral  Nebula  in  Ursa  Major  (H.  J.  Shepstowe). 


[233 


SPIRAL   NEBULAE.  233 

the  "  Great  Nebula  in  Andromeda  "  (31  M.).  Its  elliptic  outline 
is  shown  in  a  small  telescope,  and  the  nebula  is  sufficiently 
large  and  bright  to  be  seen  in  any  small  telescope  ;  but  instru- 
ments of  great  size  are  required  to  show  the  curious  details  of 
rifts  or  black  streaks  which  run  nearly  parallel  to  the  major 
axis  of  the  oval  on  the  S.  side.  Taken  as  a  whole,  the  nebula 
must  be  pronounced  as  irresolvable,  and  certainly  non-gaseous, 
and  a  considerable  number  of  isolated  stars  are  to  be  found 
within  its  limits.  There  is  no  other  elliptic  nebula  within  the 
reach  of  small  telescopes,  and  therefore  it  is  not  much  use  my 
pointing  out  that  there  are  several  which  have  double  stars  at 
or  near  each  end  of  the  ellipse,  which  in  these  cases  is  very 
elongated  compared  with  its  breadth. 

The  existence  of  the  class  of  nebulae  known  as  "  Spiral "  or 
"  Whirlpool  "  nebulae  was  first  made  known  by  the  3rd  Earl  of 
Rosse  when  he  brought  his  great  reflectors  at  Parsonstown  to 
bear  on  these  objects.  Two  or  three  in  particular  of  those 
whose  structure  was  discovered  by  him  are  well  known  because 
they  have  been  engraved  in  a  great  number  of  books  ;  but 
the  observations  and  researches  of  recent  years,  especially 
those  of  Huggins  and  Roberts,  have  rendered  it  probable  that 
masses  of  nebulous  matter,  and  indeed  aggregations  of  stars 
generally  assuming  a  spiral  form,  are  much  more  common  than 
was  supposed  when  Lord  Rosse  brought  to  an  end  his  own 
discoveries  in  this  field. 

The  two  most  important  spiral  nebulas,  determined  to  be  such 
by  Lord  Rosse,  are  those  known  as  51  M.  Canum  Venaticorum, 
and  99  M.  Virginis.  The  former  exemplifies  in  a  very  remark- 
able degree,  not  only  the  changes  which  take  place  in  the 
appearance  of  clusters  and  nebulae  according  as  they  are  viewed 
through  small  or  large  telescopes,  but  also  the  danger  of  jump- 
ing at  conclusions  and  using  dogmatic  language  in  dealing  with 
these  matters.  Figs.  288  and  289  represent  this  nebula  as 
drawn  by  Admiral  Smyth,  Sir  J.  Herschel  and  Lord  Rosse 
respectively,  whilst  Fig.  290  supplies  a  photographic  view. 


234  GROUPS    OF    STARS    AND    NEBUUE. 

Except  for  the  direct  evidence  of  the  fact  which  is  available,  it 
would  be  difficult  for  any  chance  spectator  to  suppose  that  all 
these  pictures  represented  the  same  object.  In  the  case  of 
99  M.  Virginis,  the  spiral  form  may  be  said  to  be  so  obtrusively 
obvious  in  Lord  Rosse's  sketch,  as  not  to  need  even  a  moment's 
argument.  An  inquiring  mind  will  naturally  ask  the  question, 
What  meaning  is  to  be  attached  to  the  spiral  formations  in  the 
heavens  which  are  here  brought  under  notice  ?  I  must  frankly 
admit  that  I  am  not  prepared  with  an  answer  to  this  question  ; 
which  becomes  still  more  difficult  when  we  call  to  mind  the  fact 
that  an  American  observer,  Holden,  speaking  of  a  planetary 
nebula  (presently  to  be  described),  says  that  it  "  is  apparently 
composed  of  rings  overlying  each  other,  and  it  is  difficult  to 
resist  the  conviction  that  these  are  arranged  in  space  in  the 
form  of  a  true  helix" — another  way  of  expressing  the  idea  of  a 
spiral  being  concerned. 

The  term  "planetary"  was  applied  by  Sir  W.  Herschel  to 
certain  nebulae,  small  in  number  and,  with  one  special  exception, 
small  in  size,  which  exhibit  the  appearance  of  discs  having  well- 
defined  edges,  either  circular  or  slightly  oval  and  of  uniform 
luminosity,  which  features  caused  them  to  offer  considerable 
resemblance  to  certain  of  the  planets.  97  M.  Ursae  Majoris  is 
the  most  striking  of  these,  as  it  is  also  the  largest,  for  it  has  a 
diameter  of  2'  40".  Lord  Rosse's  picture  of  it  evidently  justifies 
the  name  of  "Owl  Nebula"  which  he  gave  to  it,  albeit  his 
picture  negatives  the  general  description  of  these  planetary 
nebulas  with  which  I  started  at  the  commencement  of  this 
paragraph.  The  planetary  nebula  which  I  mentioned  just  now 
as  presenting  the  features  of  a  helix  is  37  y  IV.  Draconis,  as 
viewed  in  the  Lick  telescope  ;  but  of  course  no  ordinary  tele- 
scope will  bring  out  the  details  which  Holden  has  described. 

Planetary  nebulae  seem  to  possess  some  peculiarities  which 
differentiate  them  from  nebulae  generally.  The  great  majority 
of  them  are  situated  in,  or  close  to,  the  Milky  Way  ;  they  are 
much  more  numerous  in  the  Southern  Hemisphere  than  in  the 


FIG.  291 


PLATE   XCVL 


The  Nebula  4620  h  =  58  Itf  VIII.  Cygni  (E.  E.  Barnard}. 


1 234 


FIG.  292 


PLATE    XCVII. 


The  Nebulae  81  and  82  M.  and  a  nebulous  Star  in 
Ursa  Major  (Isaac  Roberts}. 


[235 


IRREGULAR    NEBULAE. 


235 


Northern  ;  they  are  most  of  them  gaseous,  according  to  spectro- 
scopic  observations  ;  and  many  of  them  seem  to  exhibit  a  bluish 
tinge  of  colour. 

"  Nebulous  stars  "  can  only  be  described  as  stars  which  are 
surrounded  by — or,  perhaps  it  will  be  better  to  say  which  seem 
to  be  surrounded  by — nebulous  matter  symmetrical  or  circular 
in    outline.      Hind   remarked   that   the   stars  thus   enveloped 
"  have   nothing  in  their  appearance  to  distinguish  them  from 
others  entirely  destitute  of  such  appendages."     The  brightest 
nebulous      star, 
recognised  as  such, 
is     i     Orionis,     of 
mag.    3^ ;    though 
the   star  iwhich   is 
generally  named  as 
the     most      repre- 
sentative     of      its 
class    is  45   I#   IV. 
Geminorum,  which 
Sir  John  Herschel 
described     as     an 
8th-magnitude  star 
"  exactly     in      the 
centre  of  an  exactly 
round  bright  atmo- 
sphere 25"  in  diameter."     There  are  not  many  of  these  stars 
known,  and   the   few  there    are    cannot  be   usefully  observed 
except  with  large  telescopes. 

The  6th  and  last  class  of  nebulae  which  require  notice  are 
altogether  of  irregular  form  and  large  size.  Though  most  of 
them  which  will  now  be  mentioned  are  discernible  in  small 
telescopes,  yet  here,  again,  instruments  of  great  light-gathering 
power  are  indispensable  for  their  satisfactory  examination. 

Mention  has  already  been  made  of  the  "  Great  Nebula  in 
Andromeda,"  which,  for  some  reasons,  might  with  propriety  be 


(Sir  J.  Herschel.)  (Earl  of  Rosse.) 

Figs.  293  and  294.— Planetary  Nebula  97  M. 
Ursae  Majoris. 

Generally  known  as  "  The  OwkNebula." 


236  GROUPS    OF    STARS    AND    NEBULA. 

enrolled  in  the  class  which  we  are  now  considering,  especially 
on  account  of  its  size  and  brilliancy,  and  because  its  elliptic 
form,  which  was  the  reason  for  including  it  under  the  head  of 
elliptic  Nebulas,  disappears  almost  entirely  with  optical  assist- 
ance on  a  large  scale. 

Subject  to  this  remark,  the  "Great  Nebula  in  the  Sword- 
handle  of  Orion  "  must  be  put  first  in  importance  in  any  list  of 
irregular  nebulae.  Its  size  and  brightness  led  to  its  discovery 
very  soon  after  the  invention  of  the  telescope,  and  it  has 
received  more  attention  from  the  pens  and  pencils  of  astrono- 
mers than  any  other  object  in  the  sidereal  heavens.  The  first 
feature  which  immediately  forces  itself  on  our  attention  when  it 
is  looked  at  is  the  singular  vacuity  which  is  called  "  The  Fish's 
Mouth,"  from  its  supposed  likeness  to  the  mouth  of  various  sorts 
of  fish.  This  is  no  sooner  seen  than  the  second  object  to  attract 
attention  immediately  does  so,  namely,  "The  Trapezium"of  stars, 
the  most  important  of  which  is  6  Orionis,  which,  on  account  of 
its  near  neighbours,  is  generally  spoken  of  as  a  "  multiple  star." 
The  largest  member  of  the  family  being  6,  the  use  of  the  word 
"Trapezium"  naturally  implies  that  there  are  three  other  stars 
close  at  hand  to  make  up  the  figure  which  geometricians  call  a 
trapezium  :  but  this  is  not  the  end  of  the  matter. 

Whilst  any  small  telescope  will  reveal  without  much  difficulty 
the  4  special  stars,  a  5th  and  6th  come  into  view  when  more 
telescopic  power  is  available  ;  indeed,  these  5th  and  6th 
stars  constitute  a  very  good  test  of  telescopes  of  5  or  6  or 
more  inches  of  aperture.  But  it  is  claimed  that  three  more 
stars  exist  in  or  closely  adjacent  to  the  Trapezium,  bringing 
up  the  total  number  to  9.  The  existence  of  these  3  supple- 
mentary stars  rests  especially  on  the  authority  of  Huggins,  and 
has  been  vehemently  disputed.  A  fair  summary  of  the  situation 
appears  to  be  this  :  that  there  are  other  stars  in  or  close  to  the 
Trapezium ;  that  they  are  variable  ;  and  that  the  6th  star 
itself  is  variable.  This  last  statement  seems  undoubtedly  true, 
and,  if  the  3  smaller  stars  are  also  variable,  we  have  a  com- 


FIG.  295 


PLATE    XCVIII. 


236] 


FIG.  296 


PLATE    XC1X. 


The  Great  Nebula  in  Orion  (W.  E.  Wilson}. 


[237 


THE   GREAT    NEBULA    IN    ORION. 


237 


plete  explanation  of  the  contradictions  which  have  been  indulged 
in  on  the  subject.  This  nebula,  as  a  whole,  illustrates  in  a 
striking  degree  the  discordances  which  constantly  present  them- 
selves between  hand-drawings  of  sidereal  objects  and  photo- 
graphs. The  hand-drawings  of  this  nebula  all  fail  to  do  more 
than  con- 
vey  the 
idea  of 
its  being 
a  flat 
patch  of 
nebulous 
matter. 
Or,  if  this 
s  t  a  t  e  - 
ment 
too  defi- 
nite, it 
must 
certainly 
be  said 
that  they 
fail  to 
convey 
any  suffi- 
cient in- 
d  i  cations 
of  the 
rlocculent 

texture  which  is  such  a  special  feature  of  all  the  photographs 
which  I  have  ever  seen.  It  is  the  existence  of  masses  of 
seemingly  flocculent  material  which  makes  it  so  difficult  to 
accept  the  theory  that  nebulae,  such  as  this  one,  are  masses  of 
incandescent  gas. 

The  nebula  known   as  30  Doradus  is  a  very  singular  one, 


North. 
Fig.  297.—"  The  Trapezium  of  Orion,"  Jan.  1866. 

(Huggins.) 


2.38  GROUPS    OF    STARS    AND    NEBULA. 

owing  to  the  strange  convolutions  of  the  nebulous  matter,  which 
almost  defy  description.  It  is  faintly  visible  to  the  naked  eye, 
of  course  as  a  mere  patch,  within  the  limits  of  the  Nubecula 
Major,  to  be  presently  described. 

The  nebula  surrounding  the  star  77  Argus  is  another  very 
remarkable  object — remarkable  alike  from  its  special  features  as 
well  as  its  history.  When  Sir  J.  Herschel  was  at  the  Cape  in 
1833  and  following  years,  he  gave  very  careful  attention  to  this 
nebula  and  to  the  position  of  the  chief  star  in  it.  He  specially 
pointed  out  a  void  space  in  the  middle  of  the  nebula,  and  that 
the  star  was  wholly  surrounded  by  nebulous  matter.  He 
remarked  that  "  It  is  not  easy  for  language  to  convey  a  full 
impression  of  the  beauty  and  sublimity  of  the  spectacle  which 
this  nebula  offers  as  it  enters  the  field  of  the  telescope  (fixed 
in  R.A.)  by  the  diurnal  motion,  ushered  in  as  it  is  by  so  glorious 
and  innumerable  a  procession  of  stars,  to  which  it  forms  a  sort 
of  climax."  Some  sensation  was  caused  in  astronomical  circles 
in  1863  by  a  statement,  put  forth  by  a  Tasmanian  observer 
named  Abbott,  that  the  void  space  had  altered  in  form,  and  that 
the  star  77  no  longer  had  nebulous  matter  close  up  to  it.  These 
allegations  were  proved  to  have  been  quite  unfounded,  and  it  is 
difficult  to  realise  how  Abbott  could  have  been  led  to  make 
them.  Herschel  had  published,  in  connection  with  his  obser- 
vations, a  careful  drawing  of  the  nebula,  and  it  was  found,  50 
years  afterwards,  that  his  drawing  still  represented  accurately 
the  general  appearance  of  the  object. 

The  nebula  20  M.  Sagittarii  is  the  chief  member  of  an  im- 
portant group  which,  perhaps,  would  be  better  described  as  a 
single  mass  of  nebulous  matter  pieced  together  and  exhibiting 
a  strange  shape.  Its  special  feature  is  a  "three-forked  rift  or 
vacant  area,  abruptly  and  uncouthly  crooked,  and  quite  void 
of  nebulous  light."  This  is  Sir  J.  HerschePs  description 
of  it,  and  he  goes  on  to  say  that  a  beautiful  triple  star  "  is 
situated  precisely  on  the  edge  of  one  of  these  nebulous 
masses,  just  where  the  interior  vacancy  forks  out  into  two 


FIG.  298 


PLATE    C. 


The  Nebula  surrounding  ?/  Argus  (C.  E.  Peek,  1882), 


238] 


FIG.  299 


PLATE   CI. 


[239 


NOTEWORTHY    NEBUL/E. 


239 


channels,"     This  nebula  is  sometimes  called  the  "  Trifid  Nebula 
in  Sagittarius." 

It  is  unfortunate  that  Sagittarius  should  be  a  constellation 
not  very  favourably  situated  for  observation  in  England,  for 
in  the  nebula  8  M.  Sagittarii  we  have  another  striking  object 
of  a  very  diversified  shape,  and  which  is  a  mixture  of  nebula 
and  stars  in  the  same  field.  It  is  an  interesting  question  in 
regard  to  cases  such  as  this  whether  any  relations  subsist 
between  the  nebulous  matter  and  the  stars ;  that  is  to 
say,  whether  the  stars  are 
actually  connected  with  the 
nebula,  or  are  merely  opti- 
cally superposed  in  front  of 
it.  The  question  is  one 
which,  in  general,  can  only 
be  dealt  with  as  a  matter 
of  individual  opinion.  I 
have  already  stated  on  a 
previous  page  the  strong 
conviction  that,  in  the  case 
of  the  temporary  star  which 
burst  forth  some  years  ago 
in  the  great  nebula  in 
Andromeda,  in  viewing  the  pig.  300.— The  Nebula  17  M.  Clypei 
star,  we  were  looking  at  an  Sobieskii  (Chambers). 

object  which  happened  to 

be  in  front  of  the  nebula,  and  had  no  connection  with  the 
nebulous  mass  which  we  saw  in  the  background.  The  nebula 
8  M.  Sagittarii  may  be  detected  by  the  naked  eye  ;  but,  of 
course,  a  telescope,  and  one  of  some  power,  is  needed  to 
bring  out  its  features. 

In  the  constellation  known  indifferently  as  Scutum  Sobieskii, 
or  Clypeus  Sobieskii,  we  have  a  nebula  (17  M.)  which  is  often 
called,  but  not  very  judiciously,  "The  Horse-shoe  Nebula," 
though  now  the  name  of  "The  Omega  Nebula"  is  more  gener- 


240  GROUPS    OF    STARS    AND    NEBUIJE. 

ally  and  properly  attached  to  it.  In  real  truth,  when  seen  at 
its  best,  it  takes  the  form  of  2  Greek  omegas  coupled  together 
at  their  bases  by  a  bar  of  nebulous  matter  ;  but  the  amateur 
with  a  small  telescope  must  be  satisfied  if  he  makes  out  the 
shape  of  this  object  to  be  that  of  a  swan  without  legs.  One 
needs,  in  these  days,  to  be  very  wary  of  accepting  suggestions 
of  changes  in  nebulae,  but  there  does  appear  to  be  some 
evidence  that,  within  50  years  of  Sir  John  Herschel's  careful 
record  of  the  appearance  of  this  nebula,  it  did  undergo  some 
real  change  of  form,  according  to  the  testimony  of  several 
experienced  observers  and  draughtsmen. 

The  next  obje'ct  which  comes  before  us  in  the  order  of  Right 
Ascension  is  a  very  well-known  nebula  commonly  called  "  The 
Dumb-bell  Nebula  in  Vulpecula."  The  name  is  very  appro- 
priate in  speaking  of  it  after  viewing  it  with  a  telescope  of 
moderate  size— say,  up  to  6  or  8  inches  of  aperture  ;  but 
greater  optical  power  so  completely  transforms  its  appearance 
that  the  idea  of  a  dumb-bell  quite  passes  out  of  one's  thoughts. 
The  truth  of  this  statement  will  be  readily  realised  by  an 
examination  in  succession  of  the  illustrations  given  (see  Figs. 
301-304).  In  a  small  telescope  it  appears  like  2  somewhat 
round  nebulosities  in  contact.  Sir  J.  Herschel  saw  it  with 
"an  elliptical  outline  of  faint  light  enclosing  the  two  chief 
masses";  but  Lord  Rosse's  2  reflectors  made  material  changes 
in  its  appearance.  His  3-ft.  reflector  destroyed  the  regular 
elliptic  outline  noted  by  Sir  J.  Herschel,  whilst  the  6-ft.  re- 
flector brought  about  a  still  more  striking  transformation, 
and  introduced  a  considerable  number  of  stars  individually 
recognisable  as  such. 

The  constellation  Cygnus  furnishes  a  striking  nebulous 
aggregation  (No.  4618  of  Herschel's  "  General  Catalogue  "). 
This  has  been  described  as  a  very  large  space  20'  or  30'  long 
in  Declination,  and  I  hr.  or  more  wide  in  R.A.,  full  of  stars  and 
nebula  mixed. 

The   Southern  Hemisphere   contains  2  objects,   known    re- 


FIGS.  301-302 


PLATE   CII. 


240] 


FIGS.  303-304 


PLATE   CIII. 


FIGS.  305-306 


PLATE 


Nebulous  Region  of  •>  Ophiuchi. 


Nebulous  Region  of  y  Cygni  (E.  E.  Barnard}. 
2406]    Nebulosity  not  visible  in  telescope,  but  disclosed  by  photography, 


FIG.  307 


PLATE   CV. 


The  Nebula  14  Ijl  V.  Cygni  (Lick  Observatory}. 


[240C 


FIG.  308 


PLATE    CVT. 


The  "  Trifid  Nebula  "  in  Sagittarius. 


240^1 


FIG.  309 


PLATE   CVII. 


The  "  Trifld  Nebula  "  in  Sagittarius. 


2400 


FIG.  310 


PLATE    CVIII. 


Stars  in   Cygnus  (Henry,  at  the  Paris  Observatory). 


240/J 


FIG.  311 


PLATE    CIX. 


FIG.  312 


PLATE   CX, 


FIGS.  313-314 


PLATE    CXI. 


Double  Cluster  in  Perseus. 


Black  space  void  of  stars  with  Constellation  Sagittarius. 

.[241 


DISTRIBUTION    OF    NEBULAE    IN    THE    HEAVENS.          241 

spectively  as  the  Nubecula  Major  and  the  Nubecula  Minor, 
which  are  large  patches  of  nebulous  matter  which  received 
their  names  from  their  cloud-like  appearance  and  relative  size. 
The  former  is  in  the  constellation  Dorado,  and  the  latter  in 
Toucan.  Both  are  visible  to  the  naked  eye  on  a  dark  night, 
but  the  smaller  one  is  overpowered  by  moonlight.  Sir  J. 
Herschel  described  them  as  "  consisting  of  swarms  of  stars, 
clusters,  and  nebulae  of  every  description."  The  larger  one  is 
about  four  times  the  size  of  the  smaller.  I  am  not  acquainted 
with  any  more  complete  or  modern  description  of  either. 
Unfortunately,  the  Southern  Hemisphere  seems  altogether  lack- 
ing in  astronomical  authors  who  might  write  books  describing 
what  they  had  seen  in  the  same  way  as  the  multitude  of 
European  and  American  authors  have  described,  and  continue 
to  describe,  the  celestial  sights  visible  in  the  Northern  Hemi- 
sphere. This  absence  of  literary  enterprise  on  the  other  side 
of  the  world  is  much  to  be  regretted,  and  we  still  have  to 
draw  largely  on  the  great  work  published  in  1847  by  Sir  J. 
Herschel,  in  which  he  recorded  the  results  of  his  observations 
at  the  Cape  in  1834  and  subsequent  years.1 

A  chapter  on  clusters  and  nebulae  would  not  be  complet 
without  some  allusion  to  their  distribution  in  the  sky,  which  ii 
exceedingly  irregular.  Subject  to  certain  special  exceptions, 
it  may  be  said  that  the  fixed  stars,  commonly  so-called,  are 
distributed  fairly  evenly  over  the  whole  sky  ;  but  this  is  a 
long  way  from  being  the  case  with  the  nebulas,  as  will  be 
readily  understood  by  a  simple  inspection  of  Sir  J.  Herschel's 
"  Catalogue  "  of  5079  of  these  objects,  which  was  published 
in  1864.  An  examination  of  this  volume  discloses  the  follow- 
ing striking  results.  Whilst  Hour  XII.  of  Right  Ascen- 
sion includes  686  nebulae,  including  clusters,  and  Hour  XI. 
421,  Hour  XIX.  has  only  79,  and  Hour  XX.  only  90.  In 
other  words,  the  constellation  Virgo  and  its  neighbours 

1  Results  of  Observations  made  during  the  years  1834-8  at  the  Cape  of  Good 
Hope. 

16 


242  GROUPS    OF   STARS   AND    NEBULAE. 

include  ith  of  the  total  number  of  nebulas  recorded  up  to  the 
middle  of  the  igth  century ;  and  I  do  not  suppose  the  rela- 
tive proportions  have  been  seriously  destroyed  by  the  later 
discoveries.  The  regions  nearest  to  the  Milky  Way  are 
least  abundant  in  nebulas,  whilst  the  two  richest  regions  are 
those  which  lie  at  the  2  poles  of  that  great  belt.  Another 
circumstance,  doubtless  of  significance  though  we  cannot  tell 
its  meaning,  is  that  the  great  majority  of  the  nebulas  indicated 
by  the  spectroscope  to  be  gaseous  are  situated  either  within 
or  on  the  borders  of  the  Milky  Way,  whilst  in  the  regions  near 
the  poles  of  the  Milky  Way  such  nebulae  are  scarce,  though 
there  are  plenty  of  non-gaseous  nebulae  situated  in  those 
localities. 

This  chapter  must  not  be  closed  without  a  few  words  re- 
specting the  Milky  Way  itself,  because  it  is  one  vast  nebula 
running  right  round  the  heavens  in  the  form  of  a  belt,  or  ring ; 
at  the  same  time  a  description  of  its  course,  if  put  into  words, 
would  occupy  more  space  than  is  here  available.  Any  one 
wishing  to  follow  it  right  round  the  heavens  through  the  various 
constellations  can  do  so  in  no  better  way  than  by  patiently 
going  over  the  ground  with  Sir  J.  Herschel's  well-known  Out- 
lines of  Astronomy  in  his  hands.1  It  is  long  and  elaborate, 
but  very  carefully  framed.  Suffice  it,  then,  to  say  that  the 
course  of  the  Milky  Way  conforms  nearly  to  that  of  a  great 
circle  inclined  at  an  angle  of  about  63°  to  the  Equinoctial,  and 
cutting  that  circle  in  R.A.  6h.  47m.  and  8h.  47111.  From  this 
it  follows  that  its  northern  pole  is  situated  in  about  R.A. 
12  h.  47m.,  and  Declination  27°  N.,  whilst  its  southern  pole 
may  be  considered  to  be  at  oh.  47  m.,  and  Declination  27°  S. 

Passing  over  the  numerous  and  varied  attractive  features  of 
the  Milky  Way,  which  are  too  numerous  and  too  varied  to  be 
detailed  here,  mention  must  be  made  of  a  singular  void  space 
in  the  constellation  Sagittarius,  the  precise  position  of  which 

1  Herschel's  description  has  been  reprinted  in  my  Handbook  of  Astronomy, 
4th  edition,  vol.  iii.,  and  some  other  modern  works. 


THE    MILKY    WAY.  243 

is  R.A.  17  h.  56m.,  and  Declination  27°  51'  S.  This  black  hole 
is  almost  circular,  and  on  the  N.W.  of  it  there  are  4  stars, 
the  brightest  of  which  is  orange  in  colour.  To  the  E.  of  this 
hole  there  is  another  void  space  in  the  shape  of  a  narrow 
crescent ;  but  this  space  appears  less  black  and  less  sharply 
defined  than  the  main  vacuity  previously  described. 

My  last  words  here  will  be  to  recall  the  fact  that,  strange  as 
it  may  appear,  the  idea  of  spilt  milk  is  associated  in  several 
languages  with  what  we  still  persist  in  calling  "The  Milky 
Way,"  and  that  for  centuries  upon  centuries  past  it  has  been 
the  subject  of  grotesque  nomenclature  and  fantastic  specula- 
tions. Whilst  the  grotesque  nomenclature  may  be  said  to 
have  ceased,  I  fear  it  cannot  be  said  that,  though  we  have 
reached  the  2oth  century,  fantastic  speculations  have  come  to 
an  end. 


CHAPTER   XIII. 
THE  CONSTELLATIONS. 

The  subject  one  of  great  interest. — The  best  way  of  learning  their  posi- 
tions.— The  effects  of  the  diurnal  movement. — Star-atlases  and  plani- 
spheres.— The  constellations  best  learnt  in  the  open  air. — List  of 
stars  of  the  ist  magnitude. — Standard  stars  of  the  first  4  magnitudes. 
— Alignment  of  Stars. — Origin  of  the  constellations. — Modern  addi- 
tions.— A  hasty  survey  of  the  Northern  Hemisphere. 

A  VERY  attractive  chapter  might  be  written  on  the  constella- 
tions in  history  and  poetry  with  respect  to  their  origin,  names, 
and  gradual  developement  in  numbers  during  a  period,  to  put 
it  moderately,  of  not  less  than  3000  years  ;  but  it  would  be 
foreign  to  the  design  of  this  work  to  deal  with  the  subject  from 
these  standpoints,  which  would  be  more  within  the  province  of 
the  antiquarian  than  of  the  astronomer.  The  scope  of  this 
work  is  so  essentially  to  present  the  useful  and  practical  side 
of  things  that  I  must  be  wary  of  the  temptation  to  stray  away 
from  the  limits  thus  imposed  on  me. 

An  account  of  the  constellations  in  detail  has  been  formed 
into  an  independent  chapter  (post]  to  facilitate  their  study  in  the 
open  air  with  as  little  as  possible  to  embarrass  the  student  beyond 
the  unavoidable  distractions  of  having  to  handle  a  star-atlas 
and  a  lamp.  I  thus  limit  the  suggested  impedimenta  because 
many  years'  experience  has  taught  me  the  mischief  of  trying  to 
do  too  many  things  at  the  same  time  ;  and  therefore  I  urge  very 
strongly  the  importance  of  earnest  efforts  to  become  familiar 

244 


HOW   TO   STUDY   THE   CONSTELLATIONS.  245 

with  the  constellations  in  respect  to  their  positions  and  the 
names  and  situation  of  the  principal  stars  in  each. 

It  is  not  an  uncommon  thing  for  a  writer  sitting  down  to 
describe  the  constellations  with  an  educational  idea  in  view 
to  treat  each  constellation  as  if  it  were  a  parish  in  a  county — a 
geographical  unit  standing  quite  by  itself.  This,  in  my  opinion, 
is  a  way  of  looking  at  the  constellations  which  must  be  carried 
out  with  great  discretion  and  considerable  reserve,  because  it 
is  often  apt  to  lead  to  stars  and  other  objects  being  lost  for  the 
particular  night  by  reason  of  the  diurnal  movement  taking 
them  out  of  sight  whilst  the  student  is  looking  another  way. 

What  I  mean  will  be  better  understood  if  I  put  it  in  this  way. 
When,  on  a  given  night,  an  observer  wishes  to  lay  himself  out 
for  a  night's  work,  let  him  begin  by  ascertaining  what  con- 
stellations are  on  the  meridian  when  his  work  begins,  and, 
having  just  grasped  them  generally,  let  him  begin  by  examining 
the  stars  which  are  on  the  meridian  in  the  extreme  South  (this 
for  England),  and  then  work  backwards  northwards  on  the 
same  R.A.  towards  the  North  Pole  behind  him.  He  need  not 
trouble  about  constellations  and  stars,  say,  within  30°  of  the 
Pole,  because  these  are  visible  all  the  year  round,  and  therefore 
are  always  within  his  reach  ;  but  I  do  urge  very  strongly  the 
advantage  of  working  in  accordance  with  the  hour  of  R.A., 
which  is  on  or  near  the  meridian,  and  taking  up  his  objects 
selected  for  study  as  they  severally  come  to  meridian,  and 
guarding  his  eyes  and  thoughts  from  wandering  promiscuously, 
not  only  over  the  heavens,  but  even  up  and  down  the  same 
constellation.  One  thing  is  quite  certain  :  the  constellations, 
as  regards  their  relative  positions,  can  only  be  effectively  learnt 
by  open-air  comparisons  of  the  face  of  the  heavens  with  a  star- 
map. 

Whilst  there  are  many  star-atlases  and  planispheres  in 
circulation  nowadays,  there  are  undoubted  ad  vantages  attending 
the  use  of  a  map  in  which  stars  are  portrayed  in  white  on  a 
dark  blue  or  black  background.  I  have  therefore  used  during 


246  THE    CONSTELLATIONS. 

many  years,  with  very  satisfactory  results,  the  star-maps  in 
Keith  Johnston's  Atlas  of  Astronomy  edited  by  Hind.  Next 
after  this  I  would  name  McClure's  Atlas  published  by  the 
Society  for  Promoting  Christian  Knowledge,  which  is  an 
English  edition  of  a  well-known  German  atlas,  originally  com- 
piled by  Heis  of  Miinster  ;  but  McClure  has  greatly  improved 
it  and  added  to  it.  The  stars  are,  however,  given  as  black 
points  on  white  paper.  There  is  also  given  a  deal  of  informa- 
tion descriptive  of  the  most  striking  stars  and  clusters  of  stars 
and  nebulae  which  deserve  examination. 

A  clever  American,  Dr.  C.  J.  Kullmer,  of  Syracuse,  N.Y., 
has  invented  a  "  Star-finder "  somewhat  in  the  form  of  an 
ordinary  Equatorial,  so  far  as  its  fundamental  principle  is  con- 
cerned, but  with  various  accessory  features,  and  it  has  met  with 
a  large  amount  of  acceptance  in  America,  though  I  do  not  think 
that  the  instrument  has  yet  become  known  in  England.  The 
engraving  will  indicate  its  general  form  better  than  an  elaborate 
description.  Regarded  as  an  Equatorial  in  principle,  the  arrow 
takes  the  place  of  the  telescope  tube.  The  instrument  must 
first  be  placed  facing  N.  and  the  dials  set  for  the  day  and  hour  ; 
then  the  constellations  can  be  sighted  along  the  arrow  without 
further  change.  Star-maps  on  the  dial  show  the  grouping  of 
the  stars  in  their  actual  position  as  seen  in  the  sky,  and  the 
arrow-points  at  the  constellations,  whether  they  are  above  the 
horizon  or  not,  and  if  the  desired  constellation  is  not  visible  at 
the  time,  then,  by  revolving  arrow  and  dial,  the  time  of  rising 
can  be  found.  The  instrument  stands  about  10  inches  high, 
and  the  dial  is  6  inches  in  diameter.  It  is  adjustable  to  any 
latitude  in  the  Northern  Hemisphere.  Conversely  to  finding  a 
constellation  or  bright  star  which  it  is  desired  to  find,  it  may  be 
used  to  identify  the  name  of  any  constellation  or  bright  star 
towards  which  the  arrow  is  directed.  It  also  shows  sidereal 
time,  which  is  read  off  opposite  the  graduation  for  March  21. 
An  incidental,  but  often  very  useful,  item  of  information,  which 
can  be  arrived  at  with  the  assistance  of  the  printed  instructions 


KULLMER  S    STAR-FINDER. 


247 


supplied  with  the  instrument, 
is  this  :  where  a  given  con- 
stellation or  position  in  the 
heavens  will  be  (so  far  as  the 
observer's  chance  of  seeing 
it  is  concerned)  in  the  sky  on 
a  given  day.  Such  informa- 
tion would  often  be  useful  to 
an  observer  who,  knowing 
the  expected  position,  say,  of 
a  new  comet  on  a  given  day, 
wants  to  know  whether,  and 
at  what  hour,  such  comet 
will  be  above  his  horizon  so 
that  he  may  have  a  chance 
of  seeing  it.  Were  Dr.  Kull- 
mer's  invention  to  become 
generally  known  in  England 
it  would, "I  think,  be  in  much 
request,  for  we  have  nothing 
of  the  kind  in  use  in  this 
country. 

I  will  suppose  the  reader 
to  have  made  himself  ac- 
quainted with  the  apparent 
sizes  and  positions  of  some 
of  the  stars,  and  that  he 
intends  to  get  up  the  whole 
subject  of  the  constellations 
in  a  systematic  manner.  The  means  for  doing  this  will  be 
found  in  a  chapter  specially  devoted  to  the  constellations  in 
detail,1  and  I  will  now  proceed  with  a  variety  of  general  con- 
siderations relating  to  the  stars. 

It  is  assumed  that  the  reader  is  standing  out  in  the  open  air, 

1  See  Chapter  XIII   (post). 


Fig.  315.— Kullmer's    "Star- 
finder." 


248  THE    CONSTELLATIONS. 

if  possible  in  some  elevated  position,  with  as  large  an  expanse 
of  sky,  as  clear  of  terrestrial  obstructions,  as  possible,  and  that 
he  is  armed  with  a  suitable  star-map,  and  something  in  the 
nature  of  a  bull's-eye  lantern,  which  may  be  either  of  the  common 
type,  and  burning  oil ;  or,  better  still,  that  he  has  a  portable 
electric  lamp. 

The  first  thing  to  be  attempted  is  to  try  and  identify  the 
brightest  stars,  which  are  those  of  the  ist  of  the  6  magnitudes 
which  are  regarded  as  embracing  the  stars  visible  to  the  naked 
eye.  It  will  be  useful  to  give  a  list  of  these  stars  in  two  forms  : 
(i)  in  the  order  of  brightness,  and  (2)  in  the  order  of  their  Right 
Ascension  ;  that  is  to  say,  in  the  order  in  which  they  succes- 
sively rise,  come  to  the  meridian,  and  set. 

FIRST-MAGNITUDE  STARS  IN  ORDER  OF  BRIGHTNESS. 

a  Canis  Majoris  (Siritts}. 

a.  Argus  {Canopus).     Not  visible  in  England. 

a  Centauri.     Not  visible  in  England. 

a  Bootis  (Arcturus). 

ft  Orionis  {Rigel). 

a  Aurigse  (Capella). 

a  Lyrse  (  Vega). 

a  Canis  Minoris  {Procyon). 

a  Orionis  (Betelgeuse). 

a  Eridani  (Achernar).     Not  visible  in  England. 

a  Tauri  (Aldebaran). 

ft  Centauri.     Not  visible  in  England. 

a  Crucis.     Not  visible  in  England. 

a  Scorpii  (Antares). 

a  Aquilae  (Altair). 

a  Virginis  (Spica). 

a  Piscis  Australis  (Fomalhattt). 

ft  Crucis.     Not  visible  in  England. 

ft  Geminorum  (Polhix}. 

a  Leonis  (ReguZus). 

ci  Cygni  {Deneb.}, 


STANDARD    STARS. 


249 


FIRST-MAGNITUDE  STARS  IN  ORDER  OF  RIGHT  ASCENSION. 


h.  m. 


a  Eridani  (Achernar)     .         . 

a  Tauri  {A Idebaran} 

a  Aurigse  (Capella) 

j3  Orionis  (Rtgel)   . 

a  Orionis  ( Betelgeuse)     . 

a  Argus  (Canopus] 

c  Canis  Majoris  (Siritts) 

a  Canis  Minoris  {Procyoii)     . 

ft  Geminorum  {Pollux}  . 

a  Leonis  (Regulus) 

a?  Crucis         .         .         %       . 

ft  Crucis          .... 

a  Virginis  (Spica)  . 

ft  Centauri      .... 

a  Bootis  {Arcturus} 

a2  Centauri     .... 

a  Scorpii  (Antares) 

a  Lyra  (  Vega)        . 

a  Aquilse  (Altair)  . 

a  Cygni  (Deneb.)    . 

a  Piscis  Australis  {Fomalhaut} 


The  dates  appended  are  those  on  which  the  stars  in  question 
will  be  found  on  or  near  the  meridian  at  midnight. 

It  will  be  noticed  that  these  stars  are  nearly  equally  divided 
between  the  Northern  and  Southern  Hemispheres  ;  that  10  are 
Northern  and  n  are  Southern  stars. 

Seidel  has  suggested  the  following  as  standard  stars  for  their 
respective  magnitudes  : 

Mag. 

1.  a  Aquiloe,  a  Virginis,  a  Orionis. 

2.  a  Ursse  Majoris.  7  Cassiopeiae,  Algol  (at  max.). 

3.  y  Lyrse,  5  Herculis,  9  Aquilae. 

/  p  Herculis,  X  Draconis  (too  bright). 
'    I /x  Bootis,  6  Herculis  (not  bright  enough). 

The  reader  is  recommended  to  make  himself  familiar  with  all 
the  stars  in  the  foregoing  lists,  because  those  in  the  first  list 


i  34 

~  5741 

October  17 

4  3° 

+  16  20 

November  28 

5  I0 

+  45  54 

December  8 

5  10 

-    8  18 

December  8 

5  5o 

+    723 

December  28 

6    22 

-5238 

December  27 

6  41 

-  1635 

December  31 

7  34 

+    527 

January  14 

7  39 
10    3 

+  28  14 

-t-    12  23 

January  15 
February  21 

12    21 

-6236 

March  28 

12   42 

-  59  12 

April  2 

13    20 

_  10  42 

April  it 

13  57 

-5956 

April  21 

14  ii 

+  1938 

April  24 

H  33 

_  60  28 

April  30 

16  24 

_  26  14 

May  27 

18  33 

+  3842 

June  29 

19  46 

+  838 

July  18 

20  38 

+  44  57 

July  31 

22    52 

-  30    5 

September  3 

250  THE    CONSTELLATIONS. 

will  serve  to  give  him  an  idea  of  where  the  respective  constella- 
tions and  indirectly  where  the  other  constellations  are  to  be 
found,  whilst  the  second  list  will  help  him  to  recognise  a  star 
of  a  named  magnitude  because  he  will  know  what  a  star  of 
such  a  magnitude  should  look  like. 

One  of  the  most  worrying  difficulties  which  has  to  be  faced  in 
studying  the  constellations,  is  the  varying  positions  which  they 
occupy  between  their  rising  and  setting.  This  really  amounts, 
more  or  less,  to  their  being  upside  down  at  setting,  compared 
with  what  they  look  like  when  rising.  This  inevitable  transform- 
ation is  another  reason  for  students  confining  their  attention 
as  much  as  possible  to  constellations  which  are  on  the  meridian 
at  the  time  that  study  is  going  on ;  or,  at  any  rate,  to  constella- 
tions within  a  couple  of  hours  or  so  on  either  side  of  the 
meridian.  The  fact  that  such  upside-down  changes  do  indeed 
apparently  take  place  will  be  better  realised  by  an  examination 
of  the  annexed  diagram  than  by  any  attempt  to  explain  the 
matter  verbally. 

Having  identified  a  few  conspicuous  stars,  the  student  must 
habituate  himself,  first  of  all,  to  drawing  imaginary  lines  from 
one  star  to  another,  either  literally  on  his  map  or  mentally  in 
his  head  ;  and  then  to  seeing  whether  he  can  pick  up  in  the 
heavens  a  particular  object  he  wants  by  running  his  eye  across 
the  sky  in  accordance  with  the  line  or  lines  on  his  map,  which 
he  must  mentally  reproduce  by  recalling  his  map.  This  pro- 
cess of  star-hunting  is  technically  called  "  allineation"  or 
"alignment."  It  is  obviously  difficult  to  put  in  writing  how  to 
do  it,  and  the  student  must  learn  to  do  it  for  himself  by  the 
exercise  of  thought  and  ingenuity.  For  instance,  if  he  sees 
on  his  map  that  the  distance  from  star  a  to  star  /3  in  a 
certain  constellation  is  so  much,  and  that  the  small  star  p 
which  he  wants  to  look  at  is  in  the  same  straight  line  with 
a  and  /3  and  fths  of  the  distance  beyond  /3  that  3  is  from  a, 
he  must  estimate,  by  more  than  one  attempt  perhaps  to  see, 
when  looking  up  at  the  stars,  whither  fths  forwards  from  /3 


STAR    CATALOGUES.  251 

will  take  him  :  then,  if  his  estimate  on  the  map  is  fairly  correct, 
and  if  he  is  able  to  estimate  where  fths  will  take  him  on  the 
sky,  he  will  find  that  the  star  /x  for  which  he  is  looking  is  in  the 
place  where  he  ought  to  find  it. 

This  method  of  finding  unknown  stars  by  means  of  imaginary 
lines  drawn  to  and  from  known  ones  is  the  only  means 
available  to  those  unprovided  with  an  equatorial  telescope 
with  its  customary  Right  Ascension  and  Declination  circles. 
There  are  various  popular  star-charts  and  books  with  diagrams 
in  circulation  with  suggested  lines  drawn  on  them  hither  and 
thither  between  different  stars.  Some  of  these  books  will  be 
useful  to  the  tyro,  but  it  not  unfrequently  happens  that  the  con- 
necting lines  are  engraved  too  heavily,  and  not  only  disfigure 
the  plates,  but  embarrass  the  eye  in  consulting  the  plates. 

Though  I  do  not  intend  to  give  a  detailed  statement  of  the 
constellations  on  their  historical  side,  it  may  be  well  just  to 
summarise  what  their  history  is.  It  begins,  for  my  present 
purpose,  as  far  back  as  Ptolemy,  who  flourished  A.D.  100-170  at 
Alexandria.  He  enumerated  48  Constellations,  21  of  which 
were  Northern,  12  Zodiacal,  and  15  Southern.  Tycho  Brahe, 
who  died  in  1601,  added  2.  Bayer  (he  of  the  Atlas) 
added,  or  rather  perhaps  accepted  as  additions,  12  constella- 
tions, all  of  them  Southern.  Royer,  in  1679,  added  5.  Halley, 
about  the  same  period,  added  i,  Robur  Caroli,  to  commemorate 
the  oak  of  King  Charles  II.  Flamsteed's  maps  contain  2 
constellations,  presumably  invented  by  himself;  and  Hevelius 
in  1690,  added  n.  During  the  i8th  century  no  fewer  than 
27  constellations,  nearly  all  of  them  Southern,  were  set  up  by 
Lacaille  and  others.  Many  of  these  18th-century  additions 
have  been  either  formally  or  informally  repudiated — a  fact 
which  will  explain  names  appearing  in  books  and  maps  pub- 
lished a  century  or  so  ago  which  are  not  now  to  be  found  in 
modern  maps  or  in  modern  lists. 

The  total  embraced  in  the  statement  just  made  mounts  up  to 
109.  Even  that  number  does  not  exhaust  the  names  which  have 


252  THE   CONSTELLATIONS. 

been  proposed  but  promptly  ignored.  The  situation  was  well 
summed  up  once  by  Sir  J.  Herschel,  who  caustically  wrote  as 
follows  : — "  The  constellations  seem  to  have  been  purposely 
named  and  delineated  to  cause  as  much  confusion  and  incon- 
venience as  possible.  Innumerable  snakes  twine  through  long 
and  contorted  areas  of  the  heavens,  where  no  memory  can 
follow  them  ;  bears,  lions,  and  fishes,  small  and  large,  Northern 
and  Southern,  confuse  all  nomenclature." 

Constellation  reformers  have,  as  was  to  be  expected,  sprung 
up  at  various  times,  but,  as  often  happens  with  reformers,  they 
did  not  obtain  much  thanks.  Two,  however,  stand  out 
especially  unworthy  of  thanks,  owing  to  their  reckless  and 
ill-advised  schemes  of  reform,  namely,  Dr.  B.  A.  Gould 
and  R.  A.  Proctor. 

Subject  to  reservations  which  have  already  been  laid  down, 
the  following  may  be  offered  as  a  brief  general  summary  of  the 
positions  of  certain  of  the  constellations  relatively  to  one  another.1 

We  will  start  with  Ursa  Major,  the  Great  Bear,  the  most 
conspicuous  of  the  constellations  which  never  set  in  Great 
Britain,  Canada,  and  the  Northern  States  of  North  America. 
The  tail  and  hind  quarters  consist  of  7  brilliant  stars,  4  of 
which  (a,  /3,  y,  §),  have  long  been  compared  to  a  waggon,  the 
other  3  (e,  £,  ?/)  being  the  horses  ;  or  the  7  taken  together 
make  "The  Plough,"  a  very  old  English  name.  The  hind 
wheels,  or  the  two  farthest  (/3,  a)  from  the  horses,  are  known  as 
"  The  Pointers,"  because  they  point  to  the  Pole-star  (a  Ursas 
Minoris)  at  the  tip  of  the  Little  Bear's  tail ;  and  farther  on 
straight  ahead  to  the  constellations  Cepheus  and  Cassiopeia, 
situated  in  the  Milky  Way  where  it  is  nearest  the  Pole. 
Cassiopeia  includes  several  bright  stars  so  grouped  that  they 
form  the  letter  M  or  W,  according  to  the  aspect  in  which  they 
are  viewed.  The  two  most  northerly  wheels  of  the  waggon 
(8  a,  Ursae  Majoris)  point  to  the  bright  star  Capella  (a  Aurigae), 
which  is  also  circumpolar  in  our  latitudes. 

1  Condensed  from  my  Handbook  of  Astronomy ,  vol.  iii. 


CONSPICUOUS    ISOLATED   STARS.  253 

The  stars  in  Ursa  Major  may  be  usefully  employed  as  scales 
of  distances  for  degrees  of  arc.  The  nearest  "pointer"  (a)  is 
28|°  from  the  Pole  ;  from  a  to  /3  is  5° ;  from  )8  to  y  is  8°  ;  from 
y  to  8  is  4^°  ;  from  5  to  e  is  5^°  ;  from  €  to  £  is  4^° ;  from  £  to  rj 
is  70-1 

Descending  diagonally  across  the  heavens  along  the  Milky 
Way  from  Cassiopeia  towards  Capella  we  come  to  a  Persei,  and 
a  little  farther  on  we  find  the  variable  Algol  (/3  Persei) ;  if  we 
pass  across  the  Milky  Way  in  the  opposite  direction  we  shall 
arrive  at  a  Cygni,  whilst  beyond  this  and  a  little  out  of  the 
Milky  Way  is  Vega  (a  Lyrse).  Draco  includes  a  long  chain  of 
stars  sweeping  partly  round  the  Little  Bear ;  and  in  the  space 
bounded  by  Cassiopeia,  Cygnus,  and  Draco,  is  Cepheus. 

Another  very  conspicuous  group  in  the  Northern  Hemisphere 
is  that  known  as  "The  Square  of  Pegasus."  Near  y  Pegasi, 
and  pointing  directly  towards  it,  are  two  conspicuous  stars  in 
Andromeda  (a  /3),  and  a  third  (y)  is  a  little  beyond  them. 
Andromeda,  as  a  constellation,  will  be  readily  known  by  the 
connection  of  its  a  with  the  3  stars  of  Pegasus  (a,  /3,  y)  which 
make  up  the  Pegasus  "  square." 

An  imaginary  line  through  the  Great  Bear  and  Capella  will 
reach  in  a  forward  direction  the  Pleiades  ;  and  then,  turning  a 
right  angle  towards  the  Milky  Way,  will  reach  Aldebaran  (a  Tauri) 
and  the  shoulders,  a,  y,  of  Orion.  Orion  is  the  most  striking 
constellation  in  the  whole  heavens,  comprising  as  it  does  so 

1  The  lack  of  astronomical  knowledge  in  high  places  is  amusingly  and 
strikingly  brought  out  in  a  recently  published  book  by  Professor  James  Stuart. 
Alluding  to  conversations  he  had  had  with  Mr.  Gladstone,  he  says  : — "It  was 
on  one  of  these  occasions,  on  a  bright  starlight  night,  that  Mr.  Gladstone  said, 
when  he  had  been  looking  at  the  stars,  '  Why  is  it  that  the  Great  Bear  seems 
so  much  more  frequently  in  the  sky  than  other  constellations?'  I  said, 
'  Because  it  never  sets.'  He  said,  '  Do  you  mean  to  say  that  it  never  sets?  I 
thought  all  the  stars  rose  and  set.'  When  I  explained  the  matter  to  him  it 
seemed  somewhat  of  a  new  idea,  and  he  said,  'Well,  I  think  that  explains 
Homer's  phrase,  6i|/e  Svwv,  if  applied  to  the  Great  Bear — that  is  to  say,  "  late  in 
going  down."'  Mr.  Gladstone  was  never  anything  of  a  physical  scientist." — 
J.  Stuart,  Reminiscences,  London,  1912,  p.  240. 


254  THE    CONSTELLATIONS. 

many  conspicuous  stars,  namely,  a,  -y,  in  the  shoulders,  5,  e,  £  in 
the  belt,  and  K  and  )8  in  the  legs.  Aldebaran  is  a  star  of  reddish 
tint,  and  the  most  prominent  in  the  V-shaped  cluster  of  the 
Hyades,  which  is  not  far  from  the  Pleiades.  Aldebaran,  the 
Pleiades,  and  Algol  make  the  upper,  while  a  Ceti  with  Aries 
form  the  lower  points  of  a  W.  The  head  of  Aries  is  denoted 
by  two  principal  stars  (a,  $). 

A  line  from  the  Pole-star  taken  midway  between  the  Great 
Bear  and  Capella  passes  to  a  and  3  Geminorum,  the  two  well- 
known  stars  Castor  and  Pollux  ;  continued  southwards  it  will 
meet  Procyon  (a  Canis  Minoris).  From  thence,  by  bending  the 
line  across  the  Milky  Way  and  carrying  it  as  far  again,  it  will 
reach  Sirius  (a  Canis  Majoris)  and  so  southwards  to  a  Columbas 
Noachi. 

Algol  and  a  and  /3  Geminorum  point  at  Regulus  (a  Leonis) 
the  Lion's  heart,  at  one  end  of  an  arc  with  /3  Leonis,  the  tuft  of 
the  Lion's  tail  at  the  other  end.  S.  of  and  preceding  Regulus 
is  Cor  Hydras  (a),  the  space  between  them  being  occupied  by 
Sextans. 

The  Pole-star  and  the  middle  horse  of  the  Great  Bear  (<T) 
direct  us  to  Spica  (a  Virginis)  at  a  considerable  distance,  whilst 
beyond  and  in  the  horizon  will  be  Centaurus. 

The  Pole-star  and  the  first  horse  of  the  Great  Bear  (77)  point 
nearly  to  Arcturus  (a  Bootes),  which  forms  with  Spica  and 
Regulus  a  splendid  triangle.  In  a  southerly  direction  another 
triangle  is  formed  by  Arcturus,  Spica,  and  Antares  (a  Scorpii). 

Corona  Borealis  is  nearly  in  a  line  between  Vega  (a  Lyras) 
and  Arcturus  (a  Bootis),  whilst  the  head  of  Hercules  and  the 
head  of  Ophiuchus  lie  between  Lyra  and  Scorpio.  In  the 
Milky  Way,  below  the  part  nearest  to  Lyra,  and  on  a  line  drawn 
from  Arcturus  through  the  head  of  Hercules,  is  Altair  (a  Aquilas), 
which  makes,  with  Vega  and  a  Cygni,  a  conspicuous  triangle. 
Closely  following  Aquila  is  Delphinus,  a  small  constellation  with 
9  rather  conspicuous  stars. 

Two  of  the  stars  in  "  The  Square  of  the  Pegasus,"  already 


THE  ZODIACAL  CONSTELLATIONS.          255 

mentioned  03,  a),  point,  at  double  their  distance,  southwards  to 
Fomalhaut  (a  Piscis  Australis). 

The  line  of  the  Ecliptic  may  without  difficulty  be  traced  by 
the  eye  by  means  of  the  stars  now  to  be  enumerated.  Not  far 
from  the  Pleiades  are  the  Hyades  and  Aldebaran  (a  Tauri),  a 
little  S.  of  the  Ecliptic.  To  the  N.W.  of  Aldebaran,  at  some 
distance,  is  the  chief  star  of  Aries  (a),  whilst  to  the  N.E.  of 
that  star  are  a  and  /3  Geminorum.  Regulus  (a  Leonis)  is  on 
the  line  of  the  Ecliptic,  and  Spica  (a  Virginis)  is  only  a  little 
S.  of  it.  The  Ecliptic  thus  known,  the  zodiacal  constellations 
may  be  easily  distinguished  in  their  successive  order  from  W. 
to  E.  Thus  Aries  lies  immediately  between  Andromeda  on 
the  N.  and  Cetus  on  the  S.,  the  3  constellations  reaching 
nearly  from  the  horizon  to  the  zenith  ;  Taurus  will  be  recognised 
by  the  Pleiades,  Aldebaran  (a)  and  the  Hyades  ;  Gemini  by 
Castor  and  Pollux,  (a,  j3)  ;  Cancer,  the  highest,  or  most  northerly 
of  the  signs,  by  the  cluster  Prassepe,  but  as  a  constellation, 
having  no  stars  larger  than  /3,  and  that  only  of  mag.  3!  ;  Leo 
from  the  stars  Regulus  (a)  and  Denebola  (/3) ;  Virgo  by  Spica  (a)  ; 
Libra  by  /3  (which,  however,  is  only  of  mag.  2|) ;  Scorpio  by  its 
brilliantly  red  star  Antares,  and  9  other  stars  of  the  3rd  magni- 
tude, or  brighter ;  Sagittarius,  the  lowest  or  most  southerly  of 
the  signs,  with  its  e  of  mag.  2  ;  Capricornus,  with  its  8  of  mag.  3  ; 
Aquarius,  under  the  neck  of  Pegasus,  with  no  stars  as  bright  as 
mag.  3  ;  and  Pisces,  between  Pegasus,  Andromeda,  and  Cetus, 
also  with  no  bright  stars. 

It  must  be  understood  that  the  foregoing  paragraphs  are  very 
rough  as  regards  the  information  they  give,  and  do  not  embrace 
the  constellations  of  the  Southern  hemisphere,  which  are  invisible 
in  England. 


CHAPTER   XIV. 
TELESCOPES. 

Telescopes  are  of  two  kinds. — Reflectors,  Refractors. — Various  kinds  of 
reflectors. — Brief  description  of  each. — Principle  of  a  refractor. — 
Spherical  aberration. — Chromatic  aberration. — The  opera-glass. — 
Stands  for  telescopes. — Importance  of  a  good  stand. — Equatorial 
stands. — Advantages  of  an  equatorial  mounting. — Accessories  to 
a  telescope. — Driving-clock. — Sidereal  clock. — The  housing  of  a 
telescope. — Advantages  of  an  observatory. — Detailed  description  of 
how  to  build  one. 

THIS  chapter  is  not  intended  to  be  either  a  treatise  on  optics,  or 
even  a  full  statement  of  the  different  classes  of  instruments 
used  in  astronomy. 

I  only  purpose  to  offer  some  information  likely  to  be  useful  to 
amateurs  able  and  willing  to  give  a  certain  amount  of  time  and 
lay  out  a  moderate  amount  of  money  in  the  purchase  of  instru- 
ments suitable  for  observing  some  of  the  more  easy  celestial 
objects  which  have  been  described  in  the  preceding  pages. 

TWO   KINDS   OF   TELESCOPES. 

Telescopes  are  of  two  kinds  ;  and  there  is  a  radical  difference 
between   them.     In   a   "  Reflector "  the  rays  of  light  coming 
from  a  distant  object  are  received  on  a  curved  surface  of  metal, 
or  silvered  glass,  and  reflected  back  to  a  "  focus,"  where  they 
are  viewed  by  a  subsidiary  piece  of  optical  apparatus  in  the 
nature  of  a  microscope,  and  which  is  called  an  "  eye-piece." 
In  a  "Refractor"  the  rays  of  light  are  received  by  a  glass 
256 


REFLECTING    TELESCOPES.  257 

lens,  through  which  they  pass,  and,  after  passing,  are  brought  to 
a  point  called  a  "  focus,3'  where  they  are  viewed  by  what  I  have 
called  a  sort  of  microscope,  though  its  proper  name  is  "  eye- 
piece," as  already  given. 

To  compare  reflectors  and  refractors  as  regards  their  relative 
merits  is  not  altogether  easy,  because  measurements  in  feet 
and  inches  of  each  are  not  comparable.  A  reflector  6  inches 
in  diameter  is  an  instrument  altogether  different  from  a  refractor 
of  the  same  dimensions.  Such  a  reflector  is  less  efficient,  and 
less  handy,  but,  it  must  be  admitted,  is  also  less  costly  than  its 
refractor  brother  ;  but,  notwithstanding  these  facts,  I  do  not 
recommend  reflectors,  for  several  reasons,  and  one  in  particular. 
The  mirror,  which  constitutes  the  essential  feature  of  the 
reflector,  is  difficult  to  keep  in  condition  ;  that  is  to  say,  however 
good  its  condition  at  the  start,  it  sooner  or  later  gets  out  of 
condition.  If  it  is  of  polished  metal  it  soon  tarnishes,  if  of 
silvered  glass  it  gets  dull,  and  in  either  case  it  is  troublesome 
to  get  at  either  for  moving  or  cleaning. 

As  between  one  reflector  and  another,  it  must  be  explained 
that  there  are  some  differences  which  make  reflectors  of  one 
type  not  quite  so  unhandy  as  those  of  another  type.  There  are 
4  principal  types  of  reflector  in  use,  namely,  the  "  Gregorian," 
the  "  Cassigranian,"  the  "  Newtonian,"  and  the  "  Herschelian." 
The  2  former  of  these  are  the  least  inconvenient  to  use  because 
the  mirrors,  which  are  at  the  eye-end  of  the  tube,  being  pierced 
in  the  centre,  the  observer  looks  straight  at  his  object,  whereas 
in  the  Newtonian  and  Herschelian  forms  the  eye-piece  and  the 
observer  are  at  the  side  of  the  tube,  and  therefore  there  has  to 
be  a  diagonal  reflector  inside  ;  and  the  observer,  every  time  he 
wishes  to  look  with  the  naked  eye  at  the  object  he  is  observing, 
has  to  twist  his  body  round.  A  Herschelian  reflector,  especially 
if  it  is  a  large  one,  is  still  more  troublesome  to  work,  because 
the  eye-piece  is  up  in  the  air,  and  therefore  the  observer  must 
be  there  also.  However,  Herschelian  reflectors  are  quite 
obsolete,  and  this,  to  some  extent,  is  true  of  the  Gregorian  and 
17 


258  TELESCOPES, 

Cassigranian  forms.  The  real  competition  nowadays  is  between 
Newtonians  and  refractors,  and  a  purchaser  will  have  to  exercise 
his  own  discretion  in  making  a  choice,  and  in  many  cases  will 
be  swayed  by  the  apparently  cheaper  price  of  the  Newtonian, 
whilst  ignorant  of  its  drawbacks,  some  of  which  have  been 
stated.  It  must,  however,  be  confessed  that  the  substitution  in 
recent  times  of  comparatively  light  silvered-glass  mirrors  for 
the  old-fashioned  heavy  metal  mirrors  has  done  something  to 
popularise  the  Newtonian  reflectors  of  moderately  large  size. 

A  refractor  takes  its  name  from  the  fact  that  it  receives  light 
from  an  object  on  the  outer  side,  and  brings  it  nearly  to  a  point 
called  the  "  focus."  Such  a  telescope,  in  its  simplest  form, 
consists  merely  of  a  double  convex  lens  at  one  end  of  a  tube, 
which  forms  an  image  of  the  object  to  be  viewed,  whilst  a 
second  and  smaller  double-convex  lens,  fixed  at  the  other  end 
of  the  tube,  serves  as  a  simple  microscope  to  magnify  the 
image  formed  by  the  first  lens.  The  first  is  called  the  "object- 
glass,"  whilst  the  magnifying  lens  is  called  the  "eye-piece." 
This  is  stating  the  matter  in  its  broadest  and  most  elementary 
shape,  and,  though  it  is  quite  possible  to  construct  a  telescope 
with  only  two  pieces  of  glass  combined  as  stated,  practically 
it  is  desirable  to  arrange  things  a  little  more  elaborately.  Two 
simple  lenses  combined  as  above  reveal  certain  optical  incon- 
veniences called  "  spherical  aberration  "  and  "  chromatic  aber- 
ration." The  result  of  spherical  aberration  is  that  the  object 
does  not  come  to  as  sharp  and  defined  a  focus  as  is  desirable, 
whilst  chromatic  aberration  is  indicated  by  the  fact 'that  the 
image  of  the  distant  object  on  view  is  inconveniently  fringed 
with  colour.  These  two  drawbacks,  which,  when  a  large  lens 
is  used  for  an  object-glass,  are  very  serious,  are  "  corrected  " 
(as  the  expression  is)  by  making  both  object-glass  and  eye- 
piece compound  instead  of  simple  ;  that  is,  by  forming  both 
object-glass  and  eye-piece  of  two  lenses  instead  of  one. 

On  the  right  disposition  of  these  lenses,  as  regards  the 
curvature  given  to  them,  depends  the  success  or  failure  of  the 


ELEMENTARY    IDEAS.  259 

optician's  efforts  to  cure  the  inconveniences  referred  to.  All 
this,  however,  is  very  technical,  and  does  not  concern  the 
general  reader,  who  buys  his  telescope  with  all  these  points 
worked  out  by  the  optician,  and  he  has  nothing  to  do  with 
them  except  to  pay  his  purchase-money  on  the  supposition 
that  they  have  been  properly  dealt  with.  In  all  cases,  however, 
an  intending  purchaser  will  do  well  to  consult  an  expert  friend, 
if  he  has  one  within  reach,  in  order  to  ascertain  that  both  the 
optical  part  of  his  proposed  purchase  and  also  the  metal 
working-parts  are  all  satisfactory. 

Up  to  this  point  I  have  been  talking  of  the  telescope  in  its 
simplest  form,  but  it  must  be  borne  in 'mind  that,  short  of 
a  telescope  properly  so-called,  a  not  inconsiderable  amount  of 
useful  and  profitable  astronomical  study  can  be  accomplished 
by  the  aid  of  a  common  opera-glass,  binocular,  or  field-glass. 
This  especially  applies  now  and  again  to  observations  of  comets, 
eclipses,  and  occultations.  An  opera-glass,  of  course,  is  naught 
else  but  2  small  telescopes  placed  side  by  side,  one  for  the  use 
of  each  eye.  Such  an  instrument,  in  its  common  form,  starts 
with  an  assumption  which  is  frequently  contrary  to  the  fact, 
namely,  that  both  eyes  of  an  observer  are  alike,  and  that  what 
suits  one  eye  will  suit  the  other  eye.  This  is  often  not  the 
case,  and  accordingly  in  the  better-made  and  higher-priced 
binoculars  provision  is  made,  not  only  for  eyes  being  different, 
but  for  the  centres  of  the  eyes  of  one  person  being  at  a 
different  distance  apart  compared  with  the  eyes  of  another 
person. 

In  making  preparations  for  carrying  on  astronomical  obser- 
vations the  question  turns  entirely  at  the  outset  on  the  money 
available  for  providing  the  outfit.  Of  course,  this  may  be 
anything  from  ,£5  up  to  ,£5000.  But  what  I  have  in  view 
in  these  pages  is  an  effort  to  assist  in  a  very  modest  outlay — 
say,  anything  between  £$  and  ,£100— leaving  the  question  of 
an  apartment  in  which  to  house  the  instrument  to  stand  over 
to  the  end  of  this  chapter,  and  be  dealt  with  separately. 


260  TELESCOPES. 


STANDS   FOR   TELESCOPES. 

When  asked,  as  I  often  am,  to  give  advice  as  to  the  purchase 
of  a  telescope  one  point  invariably  crops  up — the  difficulty  of 
impressing  on  an  inexperienced  purchaser  the  importance  of 
providing  his  telescope,  whatever  its  size  or  price,  with  a 
suitable  and  efficient  stand.  If  the  aperture  of  the  telescope 
is  to  be  no  more  than  2  inches,  and  the  cost  perhaps  ^10, 
the  only  stand  which  such  a  telescope  would  have,  or  want, 
will  be  a  tripod  of  some  sort,  either  entirely  of  brass  to  stand 
on  a  table  (known  as  a  **  pillar-and-claw  stand  "),  or  of  metal 
and  wood  combined  to  stand  on  the  ground.  Such  an  in- 
strument will  have  2  motions,  up  and  down  and  right  and  left. 
Now  these  motions,  quite  convenient  and  suitable  when  the 
objects  to  be  looked  at  are  terrestrial,  are  very  inconvenient 
and  unsuitable  in  dealing  with  celestial  objects,  and  for  this 
reason  :  the  stars  moving  across  the  sky  by  virtue  of  the 
diurnal  motion  (as  explained  in  Chapter  XL,  ante}  do  so 
diagonally  (or  on  the  skew),  and  a  telescope  which  normally 
moves  up  and  down  and  right  and  left  does  not  readily  lend 
itself  to  moving  askew. 

EQUATORIAL   STANDS. 

A  telescope  mounted  so  as  to  follow  the  movements  of  the 
stars  requires  to  be  tilted  so  that  the  main  part  of  the  stand 
shall  point  exactly  to  the  Pole.  This  secured,  then  one  pushing 
motion  of  the  telescope  incessantly  from  left  to  right  will  keep 
any  star  once  brought  into  the  field  of  view  continuously  in 
view,  so  long  as  the  pushing  motion  lasts.  In  other  words,  the 
stand  which  we  started  with,  whose  technical  name  is  an 
"  Alt- azimuth,"  has  been  converted  by  being  tilted  into  an 
"  Equatorial."  Various  expedients  for  this  conversion  have 
often  been  suggested,  but  they  are  rough  and  troublesome, 
and  the  intending  purchaser  of  a  telescope  had  much  better 


STANDS    FOR    TELESCOPES. 


26l 


begin  at  the  outset  by  buying  a  properly  devised  "  Equatorial 
Stand,"  as  an  apparatus  for  following  the  star  by  one  move- 
ment is  technically  called. 

The  various  stands  which  are  illustrated  in  this  chapter  will 
show  the  progressive  developement  of  stands,  from  the  smallest 
and  humblest 
"  pillar-  and- 
claw  "  up  to  the 
largest  and 
most  costly 
equatorials 
of  world  -  wide 
celebrity.  It  is 
not  contem- 
plated to  give 
any  detailed 
account  of  these 
large  instru- 
ments, but 
only  to  make 
the  reader 
acquainted  with 
such  develope- 
ments  of  im- 
provements and 
accessories  as 
will  keep  the  ex- 
penditure within  Fig.  316. — Astronomical  and  Look-out  Tele- 
the  limits,  more  scope  ("Pillar  and  Claw"), 

or  less,  of  ;£ioo. 

Two  things  come  up  for  consideration  as  soon  as  we  have 
decided  on  mounting  the  telescope  as  an  equatorial,  (i)  Shall 
the  stand  be  portable,  or  be  a  fixture  somewhere  ?  And  (2)  shall 
the  pushing  motion  required  to  keep  an  object  constantly  in 
the  field  be  given  by  hand  or  automatically  ? 


262  TELESCOPES. 

As  regards  the  stand  to  carry  an  equatorial,  such  stands,  in 
the  form  of  wooden  tripods,  are  easily  portable  when  they  are 
required  to  carry  telescopes  of  no  more  than  about  4  in.  of 
aperture.  But  an  equatorial  is  shorn  of  its  special  usefulness 
if  unprovided  with  setting  circles,  such  as  are  required  to  bring 
it  to  a  point  in  the  heavens  whose  R.A.  and  Declination  are 
known.  Even  without  circles  an  equatorial  stand  is  wasted  if 
some  fixed  marks  are  not  available  on  the  ground  out  of  doors 
on  which  to  place  the  3  feet  of  the  tripod  so  as  to  ensure  the 
main  axis  of  the  instrument  pointing  to  the  Pole,  which  is  the 
essential  principle  of  the  thing. 

This  difficulty  of  how  to  avoid  the  inconvenience  of  having 
no  assigned  position  in  which  to  set  up  the  tripod,  after  each 
time  it  is  removed,  is  sometimes  met  by  an  observer  erecting 
in  his  garden  an  iron  stand  as  a  permanency,  and  taking  out 
into  the  open  air  only  the  head  which  constitutes  the  equatorial, 
together  with  the  telescope,  every  night  whenever  he  proposes 
to  do  work.  This  condition  of  things  secures  a  certain  amount 
of  exactitude  in  getting  his  equatorial  into  its  proper  place  for 
use  ;  but  it  is  quite  evident  that,  to  carry  backwards  and  for- 
wards between  a  house  and  a  garden  a  telescope,  and  the 
important  parts  of  its  stand,  every  night  that  it  is  wanted  is 
alike  a  time-taking,  and,  for  various  reasons,  an  unsatisfactory 
procedure.  It  is  better  by  far  not  only  to  have  a  fixed  stand, 
but  to  keep  the  equatorial  head,  and  likewise  the  telescope, 
permanently  in  place,  and  cover  the  whole  by  a  structure  of 
some  sort  which  may  be  called  either  a  shed  with  a  movable 
top  or  an  observatory  with  a  revolving  dome,  which  obviously 
sounds  much  better. 

ACCESSORIES  TO  A  TELESCOPE. 

With  an  instrument  properly  housed  it  becomes  possible  to 
add,  not  necessarily  at  first,  if  funds  do  not  permit,  but  later 
on,  a  driving-clock.  This  is  simply  an  arrangement  of  clock- 


EQUATORIAL    STANDS. 


263 


work   which,    when    coupled    on  to  the   telescope   by  suitable 

means,  drives  or  pushes  the  telescope  continuously  forwards, 

so  as  to  keep  the  object  which  is  under  observation  continuously 

in    view  without 

the  necessity  of 

the     observer 

constantly 

having   to   push 

the  telescope— a 

labour  which  is 

not     only     very 

tedious,  but  one 

which      hinders 

him     using    his 

hands      for 

making  notes  or 

drawings. 

With  a  tele- 
scope equatori- 
ally  mounted, 
and  provided 
with  setting 
circles  and 
driven  by  clock- 
work, a  time- 
piece will  be 
required  ex- 
hibiting sidereal 
time  ;  in  other 
words,  announc- 
ing what  is  the 

Hour  of  R.A.  which  is  on  the  meridian  at  any  given  moment. 
Of  course,  a  properly  constructed  sidereal  clock,  graduated 
to  24  hours,  is  desirable,  but  it  is  a  luxury  ;  and  a  common 
French  dining-room  clock,  costing  £2  or  ;^3,  answers  the 


Fig.  317. — 3-inch  Portable  Equatorial 
Telescope. 


264  TELESCOPES 

purpose  of  a  sidereal  clock  if  it  keeps  fairly  good  time, 
and  if  the  owner  is  able  to  obtain  Greenwich  time  every  day 
or  two  from  a  local  post-office  or  otherwise.  In  my  early 
days  as  a  young  astronomer  I  did  a  great  deal  of  work  with 
such  a  clock  during  several  years,  and  had  no  difficulty  in 
picking  up  in  the  heavens  any  object  I  wanted  to  find,  so 
soon  as  I  had  obtained  sidereal  time  from  my  make-shift 
clock,  the  setting  circles  of  my  instrument  being  in  good 
adjustment.  The  methods  of  adjusting  an  equatorial  to  fit 
it  for  work  must  be  sought  for  in  books  specially  written  for 
the  purpose.1 


THE  HOUSING   OF   A   TELESCOPE. 

What  some  people  would  call  a  telescope-house,  as  they  would 
speak  of  a  motor-house  or  a  chicken-house,  is  scientifically 
called  an  "observatory."  Having  had  some  practical  ex- 
perience in  the  construction  of  observatories  suitable  for 
amateurs,  in  3  cases  for  myself  and  in  several  cases  for 
friends,  it  has  occurred  to  me  that  the  usefulness  of  this  book 
would  be  increased  if  it  contained  some  practical  hints  and 
suggestions  for  the  guidance  of  those  who  possess,  or  who 
intend  to  acquire,  a  telescope  large  enough  and  good  enough 
to  be  worth  a  permanent  fixed  shelter. 

My  first  essay  in  this  direction  was  in  1866,  when  I  put  up 
at  Sydenham  a  wooden  observatory,  10  ft.  square,  with  a 
revolving  roof  and  walls,  wholly  constructed  of  timber,  the 
roof  and  walls  being  covered  with  weather-boards  screwed  to  the 
jointed  timbers.  I  will  not  further  describe  this  structure,  the 
builder's  charge  for  which  was  ^58,  because  I  have  much  more 
recently  erected  at  Sydenham  what  is  more  or  less  a  facsimile 
of  it,  with  some  alterations  and  improvements  suggested  by  the 

1  See,  for  instance,  my  Handbook  of  Astronomy,  vol.  iii.,  "  Astronoinical 
Insiruments." 


FIG.  318 


PLATE   CXII, 


264] 


FIG.  319 


PLATE   CXIII. 


Equatorial  Telescope,  with  Object-glass  of  10  inches 

aperture  (Cooke).  [265 


TELESCOPE-HOUSES.  265 

experience  of  years.  Suffice  it  to  say,  regarding  the  1866 
observatory,  that  when  circumstances  compelled  me  to  go  and 
reside  in  a  different  part  of  the  country,  I  at  once  found  a 
purchaser  for  it,  who  was  much  struck  with  the  ease  and 
facility  with  which  the  whole  was  taken  to  pieces  and  conveyed 
into  Hampshire. 

In  1869  I  went  to  live  in  a  house  at  Bickley  which  had  a 
tower,  and,  by  arrangement  with  my  landlord,  I  supplied,  as  the 
roof  of  the  tower  which  he  built,  a  revolving  dome  to  cover  a 
4~in.  Cooke  equatorial.  This  dome  was  of  wood,  weather- 
boarded,  and  of  practically  the  same  design  as  the  roof  erected 
3  years  previously  at  Sydenham. 

Moving  to  East  Bourne,  in  1874,  to  a  house  of  my  own,  built 
after  my  own  plans,  I  provided  a  tower  about  50  ft.  high  as  part 
of  the  house,  the  topmost  story  of  which  was  built  and  fitted 
up  as  an  observatory,  surmounted  by  the  wooden  dome  brought 
from  Bickley.  This  eventually  covered  a  6-in.  Grubb  equatorial, 
with  which  instrument  I  carried  on  observations  during  a 
period  of  28  years. 

My  reason  for  making  the  top  of  the  tower  appurtenant  to 
the  house  into  an  observatory  was  because  my  5  years'  ex- 
perience at  Bickley  taught  me  the  great  advantage  of  so 
doing. 

Inducements  to  observe  in  cold,  wintry  weather  are  very 
much  more  effective  when  the  observer  is  able  to  walk  to  and 
from  his  observatory  under  cover ;  compared  with  a  different 
state  of  things  which  he  has  to  face  when  it  is  a  question  of 
dressing  up  in  a  greatcoat  and  other  things  preparatory  to 
walking  any  number  of  yards  in  the  open  air,  possibly  over 
damp  grass,  or  through  snow. 

Many  years  ago  a  writer  in  Nature  made  a  ridiculous 
attack  on  my  plea  for  putting  a  movable  dome  on  the  top  of  a 
high  tower,  such  as  mine  at  East  Bourne,  because,  sooner  or 
later,  the  said  roof  would  be  found  to  have  descended  into  the 
garden.  How  baseless  this  writer's  foolish  opinion  was,  is 


266  TELESCOPES. 

sufficiently  shown  by  the  fact  that  my  dome  passed  unscathed 
through  32  winters  and  summers  at  East  Bourne  in  a  situation 
very  much  exposed  to  the  full  force  of  south-westerly  gales, 
whenever  they  occurred,  no  other  precautions  being  taken  than 
two  ties  of  not  very  thick  rope.  Only  once,  during  the  whole 
long  period  named,  did  I  ever  see  the  dome  rise  off  its  ball- 
bearings to  an  extent  suggesting  that,  if  the  rope  had  not  been 
there,  it  might  have  gone  overboard.  As  a  matter  of  fact, 
often  for  many  weeks  and  months  together  I  neglected  to  tie 
the  rope,  and  nothing  happened. 

I  proceed  now  to  describe  my  fourth  observatory,  to  be  seen 
at  Sydenham,  which,  as  I  have  said  above,  embodies  previous 
experiences.  Its  revolving  dome  (by  the  way,  it  is  not  a  dome 
but  a  13-sided  polygon)  has  occupied  in  more  than  40  years 
three  different  sites,  and  its  timbers,  without  even  the  exception 
of  a  square  inch  of  surface,  are  as  sound  and  as  good  as  on  the 
day  on  which  they  left  the  carpenter's  shop  at  Uckfield,  in 
which  they  were  originally  put  together.  This  last-named  fact 
I  attribute  entirely  to  the  circumstance  that,  instead  of  following 
the  usual  trade  custom  of  giving  outside  woodwork  2  or  3 
coats  of  paint  all  at  once  at  long  intervals  of  time,  I  made  it  a 
rule,  as  far  as  possible,  to  put  on  a  single  coat  of  paint  something 
like  every  second  year. 

It  will  be  useful  to  explain  the  successive  steps  involved 
in  the  erection  of  an  observatory,  taking  the  reader  through 
the  actual  modus  operandi  based  on  the  fiction  that  I  am 
describing  an  entirely  new  structure,  and  not  one  a  portion 
of  which  had  actually  been  erected  previously  somewhere 
else. 

A  good  solid  foundation  is  a  sine  qua  non  to  start  with,  for 
without  it  a  telescope  of  any  considerable  weight  will  constantly 
be  getting  out  of  adjustment,  even  though  there  may  be  no  risk 
of  it  and  its  house  toppling  over.  The  extent  of  the  care  which 
it  is  expedient  to  spend  over  foundations  is  largely  a  geological 
question.  A  rocky,  gravel,  or  chalk  soil  is  usually  very  stable, 


FIG.  320 


PLATE   CXIV. 


Standard  Photographic  Equatorial,  for  the  International  Survey 
of  the  Heavens  (Sir  H.  Grubb). 


266] 


FIG.  321 


PLATE   CXV. 


27-inch  Refractor  of  the  Vienna  Observatory  (Sir  H .  Grubb). 

[267 


A    SIMPLE   OBSERVATORY.  267 

except  that  rock  is  often  very  susceptible  to  changes  of  tem- 
perature, but  this  would  not,  as  a  rule,  involve  inconvenient  or 
dangerous  settlements.  It  is  far  otherwise,  however,  with  a 
clay  soil.  This  is  a  very  trying  soil  to  deal  with  where  the 
stability  of  a  structure  of  great  weight  has  to  be  secured  in  a 
limited  area,  such  as  the  pier  of  an  equatorial  weighing  any- 
thing from  a  quarter  of  a  ton  to  2  or  3  tons.  The  soil  at 
Sydenham  is  a  stiff  clay,  which  at  different  seasons  of  the 
year  is  either  very  wet  and  sticky  or  hard  and  dry  and  full  of 
fissures.  Accordingly,  to  prepare  for  an  observatory  the  plan 
of  which  was  to  be  a  square  10  ft.  on  each  side,  I  excavated  a 
space  1 2  ft.  square  and  9  in.  deep,  and  filled  the  same  with 
77  navvy  barrow-loads  of  cement-concrete  composed  of  broken 
stone,  fragments  of  brick,  old  glass,  and  crockery,  and  indeed 
of  any  hard  rubbish  for  which  I  had  no  use,  and  which  I  wanted 
to  get  rid  of. 

This  concrete  foundation  was  left  untouched,  as  it  happened, 
for  about  3  months,  an  interval  amply  sufficient,  of  course,  to 
test  its  stability.  On  this  concrete  bed,  a  square  enclosure  of 
brickwork  was  built  in  the  form  of  a  dwarf  Q-inch  wall  of  8 
courses  of  bricks,  the  topmost  one  being  formed  of  bricks 
on  edge  set  in  cement. 

Of  course  it  will  be  understood  that  so  extensive  a  concrete 
foundation  as  that  which  I  provided  is  quite  unnecessary  in 
a  general  way,  and  that  the  only  place  where  concrete  is 
necessary  by  way  of  foundation  is  under  the  centre  of  the 
observatory,  that  it  may  serve  as  a  base  for  the  brickwork 
pillar  which  is  to  carry  the  iron  stand  of  the  equatorial, 
presuming  that  the  telescope  is  to  be  mounted  equatorially  in 
the  German  fashion.  Whether  or  not  the  walls  require  to  be 
built  on  concrete  must  depend  on  local  circumstances. 
Ordinarily  it  will  not  be  necessary  for  observatories  of  the 
type  with  which  this  section  is  intended  to  deal. 

I  will  now  give  particulars  of  my  foundations.  I  may  as  well 
remark  that  the  large  quantity  of  rough  core  which  I  used  was 


268  TELESCOPES. 

rather  because  I  had  it  and  wanted  to  get  rid  of  it,  than  because 
it  was  really  necessary. 


FOUNDATIONS. 

The  following  are  particulars  of  the  foundations,  and  of  the 
cost  of  the  same  : — 

£    s-    d. 

Excavation  of  108  cubic  feet  (labour)    .         .         .     o     12     o 
Concrete  : 

77  barrow-loads  of  broken  stone,  etc.      .  I      10     o 

5  bags  of  cement 16    o 

Labour 170 

45° 


BRICKWORK  IN  WALLS  AND  FLOOR. 

The  foundations  being  finished,  the  next  thing  to  be  done 
was  to  build  a  dwarf  wall  running  round  four  sides  of  a  square 
loft,  across.  This  wall  received,  in  my  case,  only  the  four-sided 
wooden  frame  which  constituted  the  walls  of  the  observing- 
room;  but  in  ordinary  cases  this  wall  would  be  called  upon  to 
carry  the  joists  of  the  floor  of  the  said  room.  I  preferred,  how- 
ever, at  Sydenham  not  to  have  a  wooden  floor,  but  to  form  a 
floor  by  means  of  an  additional  layer  of  concrete,  rising  about 
6  in.  inside  the  quadrangular  enclosure  formed  by  the  brick  wall 
and  brought  to  a  smooth  surface  by  cement.  The  advantage 
of  such  a  surface  for  an  observatory  floor  is  the  facility  with 
which  observing  chairs  or  stools,  or  indeed  seats  of  any  kind, 
can  be  pushed  hither  and  thither  ;  for  a  boarded  floor,  especially 
one  formed  of  imperfectly  seasoned  boards  (as  is  often  unavoid- 
able when  economy  has  to  be  considered),  is  very  inconvenient 
and  disagreeable.  A  concrete  floor  is,  moreover,  more  easily 
cleaned  and  kept  clean.  The  one  only  objection  is  that  it  is 
cold  to  the  feet,  but  this  can  be  got  over  by  having  a  mat  or 


FIG.  322 


PLATE    CXVI. 


Eye-end  of  the  Vienna  Refractor. 


268] 


FIG.  323 


PLATE    CXVI1, 


30-inch  Refractor  of  the  Pulkova  Observatory  (Repsold}. 


[269 


DETAILS    OF    A    SIMPLE    OBSERVATORY.  269 

two,  capable  of  being  moved  from  place  to  place  at  pleasure. 
The  following  was  the  cost  of  the — 

CONCRETE  FLOOR. 

£    s.    d. 

34    barrow-loads    (say   50   cubic  feet)   of  coarse, 

broken  stone  .  .  .'-•-.  .  .  .  r  14  o 
31  barrow-loads  of  small  broken  stone,  or  gravel  .  I  18  9 
Mortar,  composed  of  6  barrow-loads  of  sand,  i|- 

bags  of  lime,  and  a  little  cement  .  .  .067 
5  bags  of  cement  for  top  dressing  .  .  .  .100 
Labour 2710 


The  above  cost  includes  a  few  bricks,  and  some  cement  and 
labour,  for  fixing  the  door-frame,  building  the  pillar  for  the 
equatorial  stand,  and  two  steps  outside  the  observatory. 

The  lower  walls  were  formed,  as  has  been  already  stated,  of 
8  courses  of  red  bricks  in  9  in.  work,  the  topmost  course  being 
bricks  on  edge.  The  two  first  courses  in  the  ground  were  of 
common  stock  bricks,  being  cheaper  than  the  Sussex  red  bricks. 
The  pier  to  carry  the  equatorial  was  circular  and  raised 
21  inches  above  the  surface  of  the  floor,  and  was  surmounted 
by  a  circular  piece  of  York  stone. 

The  cost  of  this  brickwork,  exclusive  of  the  pillar,  may  be 
exhibited  as  follows  : — 

BRICKS  AND  MORTAR  FOR  THE  JOB. 

£    s.    d. 

1 100  red  bricks 3       5     o 

200  stock  bricks .         .         .         .         .         .         .070 

18  barrow-loads  of  sand  (ITJ  cubic  yards) .         .     o     12     o 
4|  bags  of  lime  (|  cubic  yard)  .         .         .         .     o       4  10 

Labour 3     16     o 

S       4   10 

We  have  now  to  consider  the  upper  (wooden)  walls  of  the 
observatory.  These  are  formed  of  upright  and  horizontal 


270  TELESCOPES. 

timbers,  4  inches  square  in  section.  The  uprights  are  12  in 
number,  tied  together  at  the  top,  in  the  middle,  and  at  the 
bottom.  The  actual  construction  consists  of  4  frames  put 
together  in  the  first  instance  as  independent  frames  and  then 
joined  together  by  strong  bolts  with  nuts.  All  the  frames  are 
6ft.  high;  2  of  them  are  loft.  8  ins.  long  and  the  other  2 
(which  fit  into  these)  are  loft,  long,  so  that  when  all  4  are 
fastened  together,  and  in  their  places,  the  external  length  of 
each  side  of  the  square  is  10  ft.  8  ins.  Each  of  the  sides  is  tri- 
sected by  means  of  the  uprights.  In  the  centre  third  of  one 
side  a  door  is  hung.  The  upper  half  of  the  centre  third  of 
2  of  the  other  sides  is  appropriated  to  a  window,  whilst  the 
fourth  side  is  covered  throughout. 

As  regards  the  outer  covering  of  the  walls,  I  had  some 
difficulty  in  making  up  my  mind.  In  my  first  Sydenham 
observatory  the  walls  were  weather-boarded,  and  painted 
inside  and  out.  Weather-boarding  is  a  perfectly  satisfactory 
method  of  covering  a  frame,  but  at  Sydenham,  in  1908,  I 
decided  on  using  galvanised  corrugated  iron,  as  much  more 
quickly  put  up  and  much  cheaper.  I  considered  the  possibility 
of  using  uralite,  but  rejected  it,  as  I  found  that  the  fixing  of  it 
would  be  troublesome.  In  an  observatory  erected  in  the  Isle 
of  Wight  by  a  relative  of  mine,  and  on  very  much  the  same 
principles  of  construction,  the  outer  covering  of  the  frame-work 
was  upright  match-boarding,  with  the  usual  grooves  and 
tongues.  This  also  is  a  perfectly  satisfactory  covering  where 
time  and  cost  have  not  to  be  studied,  and  where  material  of 
good  quality  can  be  obtained.  In  my  Sydenham  observatory 
the  frames  are  not  covered  at  all  inside,  and  I  think  they  are 
best  left  uncovered.  Of  course,  the  effect  of  covering  the 
framework  is  pleasant  to  the  eye,  but  on  the  other  hand  it 
renders  more  difficult  the  problem  of  keeping  the  inside  and 
outside  temperature  of  an  observatory  equable,  which  is  a 
matter  of  much  importance,  to  secure  the  good  definition  of 
objects  seen  through  any  telescope. , 


FIGS.  324-325 


PLATE   CXVIII. 


I 

o 

EC 

II 

CM    X 

oo 

IS 
o  o 


.2° 


$ 


270] 


FIG.  326 


PLATE   CXIX. 


36-inch  Refractor  of  the  Lick  Observatory  (Warner  &  Swasey}. 


[271 


FURTHER    DETAILS.  27 1 

UPPER  WALLS. 

£    *    d. 
Timber  frame-work,  door,  2  windows   .         .         .       8  10     o 

Lock  and  sundry  fittings 099 

17  pieces  of  galvanised  corrugated  iron  (6'  x  2') 

and  screws 11211 

Labour  for  fixing  the  wall-work     .         .         .         .118 

ii   14     4 

The  entrance-door  is  on  the  N.  side,  and  there  are  windows 
on  the  E.  and  W.  sides.  These  supply  adequate  light,  and 
may  be  regarded  as  away  from  what  is  normally  the  windward 
or  stormy  points  of  the  compass,  so  far  at  least  as  the  South 
of  England  is  concerned.  The  windows,  each  about  2  ft. 
square,  open  as  casements,  with  hinges  on  the  upper  side. 
Hung  in  this  way,  not  on  the  right  or  left  sides,  as  is  usual  with 
casements,  the  windows,  even  when  open,  do  not  generally 
allow  rain  to  blow  in  if  it  should  so  happen  that  they  have  been 
left  open  and  rain  comes  on  during  the  observer's  absence. 

Use  is  made  of  the  transverse  ties  of  the  framework  of  the 
walls  by  treating  several  of  them  either  as  they  are,  as  shelves, 
or  as  supports  for  shelves  of  greater  width  than  the  4  in. 
of  the  ties  themselves  ;  but  4  in.  is  quite  sufficient  for  a  shelf 
to  accommodate  most  of  the  loose  articles  which  are  required 
inside  an  observatory,  except  the  larger  books  and  such  things 
as  boxes  containing  eye-pieces,  etc. 

The  clock  is  placed  in  the  S.W.  angle  of  the  observatory. 
It  may  be  described  as  a  very  good  ordinary  regulator, 
showing,  of  course,  sidereal  time,  with  a  secondary  dial  gradu- 
ated to  24  hours.  It  was  made  by  a  very  first-rate  London 
clockmaker,  now  deceased,  who,  I  think,  had  never  heard  of 
a  sidereal  clock ;  anyhow,  had  never  made  one  until  he  made 
mine  under  my  supervision.  It  cost  ^28,  and  often  goes  for 
many  weeks  with  a  rate  of  about  a  second  a  day — not  bad,  for 
what  I  may  call  a  merely  civilian  clock. 


272  TELESCOPES. 

At  East  Bourne  I  used  to  rate  it  by  means  of  a  transit 
theodolite  discarded  from  the  Ordnance  Survey,  and  which  I 
therefore  picked  up  cheap  ;  but  now  at  Sydenham  I  have  no 
transit  instrument,  or  even  a  substitute  for  one,  as  I  find  it  easy 
enough  to  convey  the  time  from  the  Westminster  clock  every 
few  days  by  means  of  a  good  watch  with  a  second's  hand. 
This  celebrated  clock,  as  is  well  known,  is  seldom  more  than 
i  second  wrong.  The  time  thus  obtained  and  imparted  to  my 
clock  after  an  interval  of  an  hour  or  two  is  never  sufficiently 
wide  of  the  exact  time  to  cause  any  difficulty  in  finding  a 
celestial  object  by  means  of  the  equatorial,  my  meridian  being, 
it  is  to  be  remembered,  only  by  a  very  little  difference  W.  of 
Greenwich. 

Proceeding  onwards,  and,  as  a  literal  fact,  upwards  in  the 
construction  of  the  observatory,  the  next  and,  in  a  certain 
sense,  final  matter  is  the  roofing-in,  and  this  is  the  most 
difficult  and  troublesome  matter  of  all.  It  is  so  because  a 
revolving  top  (commonly  called  a  dome,  though  in  small  ob- 
servatories it  is  seldom  such),  the  plan  of  which  is  a  circle,  or 
a  polyhedron  rising  from  a  circle,  has  to  be  arranged  to  work 
on  the  top  of  the  square  of  the  walls.  It  is  in  effect  a  circle 
inscribed  in  a  square,  to  use  the  language  of  geometry,  which 
has  to  be  dealt  with,  and  it  is  self-evident  that  the  circle  must 
be  so  contrived  that  it  has  a  bearing  on  the  middle  of  the 
straight  sides  of  the  square,  which  means,  of  course,  that 
the  4  corners  of  the  square  obtain  no  cover  from  the  domed 
roof. 

In  order  to  obtain  as  stable  a  bearing  for  the  dome  as  possible, 
the  angles  of  the  wall-frames  are  tied  by  substantial  pieces 
of  timber,  which  convert  what  was  a  quadrangle  into  a  not 
quite  regular  octagon.  If  this  conversion  is  judiciously  carried 
out  by  the  joiner  the  effect  is  that  the  revolving  dome  is  pro- 
vided with  a  substantial  bearing  which  is  practically  circular 
and  continuous. 

The  corners  mentioned  above  as  exposed  to  "the  sky  have 


FURTHER    DETAILS.  273 

to  be  filled  in  with  a  water-tight  roof.  This  is  best  done  by 
providing  a  triangular  ceiling  at  each  corner  of  match-board 
covered  with  lead,  turned  up  about  2  inches  against  the  channel- 
plate  (to  be  described  presently),  and  turned  down  over  the 
edge  of  the  walls  to  an  extent  sufficient  to  prevent  rain  being 
blown  up  under  the  lead.  An  overlap  of  2  inches  should  in 
general  suffice,  unless  the  building  is  in  a  very  exposed  situa- 
tion. I  have  used  lead,  and  recommend  it,  because  it  is,  of 
course,  water-tight  if  put  on  by  a  competent  plumber,  and  can 
be  used  again  if  the  observatory  has  to  be  removed  to  another 
locality.  It  is  true  that  lead  is  expensive,  and  cheaper  materials 
may  be  employed,  such  are  sheet-zinc,  tarred  felt,  and 
painted  canvas,  including  Willesden  canvas  ;  but  these  materials 
can  never  be  removed  for  use  a  second  time,  and  the  3  last- 
named  are  not  only  perishable  in  a  general  sense,  but  are 
difficult  to  keep  in  water-tight  repair. 

Here  it  may  be  remarked  that  an  eaves-gutter  to  carry  off 
the  rain  which  falls  on  the  roof  may  perhaps  be  deemed  by 
some  persons  to  be  desirable,  but  this  is  a  refinement  which 
I  have  not  adopted,  because  the  rain-water  which  falls  on  the 
roof  runs  downwards  more  or  less  clear  of  the  walls  to  the 
concrete  footings  of  the  brick  wall  outside  the  building,  whence 
it  finds  its  way,  by  gravitation,  to  an  ordinary  storm-water 
garden  drain  some  6  feet  below  the  level  on  which  the  observa- 
tory is  built. 

FLAT  PART  OF  ROOF. 

The  cost  of  the  flat  roofing  at  the  corners  just  described  was 
as  follows  : 

£    s.    d. 
60  ft.  run  of  6-in.  match-boarding  .         .         .         .076 

Labour  (carpenter) o     19   II 

71  sq.  ft.  of  3-lb.  lead 219 

Labour  (plumber) 0166 

Nails,  screws,  and  other  materials          .         .         .016 


18 


274  TELESCOPES. 

THE  DOME. 

We  now  come  to  the  most  troublesome  feature  in  every 
observatory— the  construction  and  movement  of  the  dome. 

On  the  top  of  the  4  walls  and  on  the  continuous  bearing 
already  mentioned  there  is  fixed  a  circular  wall-plate,  as  it  is 
called  by  the  builders.  This  plate  is  formed  of  timber  put 
together  in  pieces  about  2  ft.  in  length,  so  that  when  they  are 
all  fitted  together  they  shall  make  a  ring  9  ft.  8  in.  in  its  internal 
diameter,  and  loft.  4  in.  in  its  external  diameter;  in  other 
words,  the  width  of  the  rim  is  4  in.  On  the  top  of  this  are 
fixed  segments  of  a  circle,  9  in  number,  of  cast-iron,  slightly 
hollowed  in  the  middle,  with  a  rim  i^in.  high  on  the  outside, 
and  somewhat  less  on  the  inside.  Thus  is  formed  a  sort  of 
circular  tramway,  in  which  3  or  more  iron  spheres  or  old- 
fashioned  cannon-balls,  about  4  in.  in  diameter,  run.  These 
permit  the  rolling  movement  of  the  dome. 

I  have  only  3  such  balls  for  the  loft,  dome,  but  4,  or  even  5, 
might  perhaps  be  better.  They  would,  however,  only  be 
better  if  they  were  all  very  truly  identical  in  diameter.  It  is 
doubtful  whether  5  such  balls  could  be  obtained  in  simple 
cast-iron  ;  they  would  have  to  be  turned  to  a  given  diameter 
in  a  lathe  by  a  competent  workman,  which  would  involve  a 
good  deal  of  extra  expense  beyond  the  cost  of  the  simple 
casting.  Yet,  unless  they  were  true  spheres  and  of  identical 
diameter  to  a  nicety,  they  would  be  useless  for  distributing 
the  weight  of  the  dome  over  the  additional  points  of  bearing 
beyond  the  bearing  afforded  by  the  3  balls  with  which  one 
started. 

It  should  be  added  that  even  3  balls  have  a  tendency  to 
get  together,  however  carefully  they  may  have  been  started 
with  an  angular  interval  between  them  of  120°.  I  find  it  a 
good  plan  to  mark  on  the  dome  itself  inside,  or  on  the  circular 
wall-plate,  points  which  are  120°  apart,  and  now  and  again 
to  bring  I  ball  up  to  one  of  these  marks,  and  then  see  how 


FIG.  327 


PLATE   CXX. 


W//      %ejgg|L^ 


36-inch  Refractor  of  the  Lick  Observatory  (Warner  &>  Swasey). 


2741 


FIG.  328 


PLATE    CXXI. 


Eye-end  of  the  Lick  Refractor. 


FIG.  329 


PLATE   CXXII. 


2746] 


FIG.  330 


PLATE   CXXIII. 


[275 


THE  ROOF  OF  THE  OBSERVATORY.         275 

far  the  other  2  balls  have  got  away  from  what  should  be  their 
marks.  When  the  displacement  has  become  considerable  it 
should  be  rectified  by  prising  up  the  dome  (with  a  strong  lever, 
such  as  a  piece  of  quartering),  so  as  to  set  free  the  2  displaced 
balls,  which  can  then  be  moved  backwards  or  forwards  to  their 
proper  positions.  It  is  obvious  that  if  the  balls  get  very  much 
displaced,  so  that,  say,  the  interval  between  2  of  them  has 
become  as  much  as  160°  or  180°,  a  very  great  strain  is  put 
upon  the  dome,  which  will  tend  to  overbalance  itself,  and  come 
down  upon  the  iron  channel-plate  so  as  eventually  not  to  be 
movable  at  all,  even  under  the  most  powerful  manual  pressure. 

The  construction  of  the  dome  is  the  most  difficult,  and  indeed 
the  only  difficult,  part  of  the  whole  undertaking.  We  have, 
first  of  all,  to  start  with  a  cill,  on  which  the  roof  has  afterwards 
to  be  built  up.  It  is  absolutely  necessary  that  this  cill  should 
be  very  strong  and  rigid,  because  it  has  not  only  to  sustain  the 
weight  of  the  rafters  and  roofing  of  the  dome,  but  also  to  stand 
the  strain  due  to  the  fact  that  the  whole  of  the  superincumbent 
weight  rests  on  only  3  points  (i.e.  balls),  and,  moreover,  is 
subject  to  the  strain  which  naturally  arises  each  time  that  the 
dome  is  pushed  round  on  its  ball-bearings. 

When  the  diameter  of  the  cill  is  no  more  than  about  8  ft.  the 
cill  may  be  best  made  of  5  or  6  layers  of  i-in.  boarding,  cut  in 
segments  and  glued  and  screwed  together,  the  joints  of  each 
one  of  the  5  or  6  rings  thus  superposed  breaking  joint  with  the 
ring  on  either  side  of  it,  until  the  desired  thickness  is  arrived 
at  by  the  requisite  number  of  rings.  On  the  inside  of  the 
composite  ring  thus  built  up  a  band  of  sheet-iron  may  be 
fastened  by  way  of  giving  further  stiffness. 

As  the  diameter  of  my  dome  was  more  than  8  ft.,  to  wit, 
10  ft.,  I  had  the  foundation  cill  of  the  dome  constructed  some- 
what differently.  Instead  of  its  consisting  of  one  ring  of  5  or  6 
layers  of  wood  in  contact,  it  consists  of  2  rings,  each  of  one 
thickness  of  stout  timber,  2|  in,  thick,  separated  from  one 
another  by  stout  upright  ties  7  in.  long,  and  secured  on  the 


276  TELESCOPES. 

upper  side  and  on  the  lower  side  by  coach-screws  countersunk 
on  the  lower  side.  This  gives  a  very  strong  and  substantial 
compound  ring  on  which  to  build  up  the  roof. 

To  the  underside  of  the  foundation  cill,  however  it  may  be 
constructed,  2  concentric  rings  of  iron  are  fixed  by  screws 
passing  through  holes  in  the  iron  rings.  The  holes  for  the 
screws  must  be  countersunk.  These  rings  must  be  carefully 
forged,  or,  better  still,  be  made  of  rolled  iron  about  i  in.  wide 
and  ^  in.  thick.  The  central  point  between  these  2  rings, 
when  fixed  to  the  wooden  cill,  and  the  central  point  of  the 
hollow  channel  in  the  fixed  plate  (already  described)  of  the 
main  building,  must  coincide  exactly — that  is  to  say,  must  be 
circumferences  of  circles  of  absolutely  identical  radius.  Unless 
there  is  this  absolute  coincidence  there  will  be  great  and 
inconvenient  friction  when  the  dome  comes  to  be  turned  round 
on  its  ball-bearings.  It  is  this  part  of  the  whole  observatory 
which  most  requires  careful  setting  out  and  good  workmanship. 

From  the  upper  side  of  what  I  have  called  the  foundation 
ring  rise  the  rafters,  14  in  number.  These  do  not  meet  in  what 
is  called,  in  an  ordinary  roof,  the  ridge-piece,  but  at  various 
points  in  a  rectangular  framework,  about  2  ft.  by  I  ft.  6  in.,  the 
exact  size  depending  in  every  case  upon  what  is  wished  to  be 
the  pitch  of  the  roof,  and  the  width,  when  open,  of  the  shutters. 
The  fourth  side  of  the  rectangle  is,  so  to  speak,  non-existent — 
that  is  to  say,  it  is  formed  by  a  cross-bar  of  iron,  set  edgeways, 
so  as  to  block  as  little  as  possible  of  the  sky  when  the  telescope 
is  directed  to  that  part  of  the  sky  which  lies  behind  the  bar. 
Two  shutters,  meeting  one  another  half-way,  rise  on  hinges 
attached  to  2  adjacent  rafters,  which,  of  course,  for  that  pur- 
pose, are  arranged  parallel  to  one  another.  The  rectangular 
frame,  which  is  supported  by  the  rafters,  constitutes  a  flat  roof 
to  the  dome. 

In  order  that  the  telescope  may  be  able,  on  occasions,  to  be 
pointed  to  the  zenith,  this  flat  roof  is  made  to  open  on  hinges 
at  the  back  (i.e.  away  from  the  shutters),  and  is  guided  up  and 


FIG.  331 


PLATE   CXXIV. 


Equatorials  under  Construction  at  the  Dublin  Works,  1912  (Grubb}. 

No.   i  for  the  Johannesburg  Observatory  ;    Object-glass  26  inches. 
276]       No.  2  for  the  Santiago  Observatory,  Chili ;  Object-glass  24  inches. 


FIGS.  332-333 


PLATE   CXXV. 


l 


IS 

CO 


THE    ROOF    OF   THE    OBSERVATORY.  277 

down  by  having  2  iron  quadrants  working  through  iron  catches, 
motion  being  imparted  by  a  pair  of  ropes  running  through 
pulleys  inside  the  sloping  roof.  The  flat  roof  is  covered  with 
thin  lead,  and  the  hinges  are  protected  by  large  pieces  of 
leather  running  all  along  the  back-side,  and  made,  as  far  as 
possible,  waterproof  by  means  of  paint.  By  the  foregoing 
arrangement  the  flat  roof,  or  lid,  of  the  dome  (as  perhaps  it  had 
better  be  called)  may  be  raised  from  the  horizontal,  through 
90°,  to  the  vertical  ;  but  I  rarely  raise  it  so  much,  not  wishing 
to  strain  the  leather  covering  of  the  hinges. 

In  order  to  open  the  2  main  shutters,  the  lid  has  to  be  raised 
3  or  4  in.  to  get  it  clear  of  the  shutters.  Special  provision  is 
made  by  grooves  on  each  side  of  each  shutter  to  keep  out  the 
rain,  or,  rather,  to  allow  any  rain  which  gets  in  to  run  down. 

The  shutters  can  be,  and  often  are,  arranged  on  a  different 
plan,  whereby  they  do  not  lift  but  slide,  one  sliding  to  the  right, 
one  to  the  left  ;  or  the  two  are  replaced  by  one  which  may  be 
constructed  to  slide  either  to  the  right  or  to  the  left  as  may  be 
wished.  The  lid  also,  in  this  form  of  construction,  slides  on 
bearings  of  its  own,  formed  as  a  framework  outside  the  sloping 
roof.  I  have  never  been  called  upon  to  manipulate  shutters 
arranged  in  this  fashion,  and  therefore  cannot  speak  from 
personal  knowledge  of  them  ;  but  I  should  fancy  that  it  was 
more  difficult  with  such  shutters  to  exclude  the  rain  than  with 
shutters  such  as  I  have  at  Sydenham.  At  any  rate,  my  lid, 
which  was  constructed  to  slide  in  this  way,  I  had  altered  at 
once  to  its  present  form. 

There  is  yet  another  form  of  shutter  which  has  some  advan- 
tages in  windy  situations.  It  really  consists  of  two  shutters, 
but,  instead  of  lifting  in  two  halves,  or  sliding  to  the  right  or 
left,  as  just  described,  it  slides  up  and  down  ;  and  when  down — 
that  is,  open  for  use,  projects  downwards,  overhanging  the 
eaves  of  the  building.  This  is  very  inconvenient.  If  up-and- 
down  shutters  are  to  be  employed  at  all,  they  had  better  be 
so  arranged  as  never  to  uncover  more  than  half  the  opening 


278  TELESCOPES. 

in  a  vertical  direction.  In  other  words,  to  open  the  observatory 
for  use,  the  upper  half  of  the  shutter  must  slide  down  over  the 
lower  half ;  or  the  lower  half  must  slide  up  behind  the  upper 
half. 

This  method  of  procedure  is  open  to  the  objection  (which  in 
certain  temperatures  of  the  atmosphere  is  very  real)  that  it 
limits  the  ventilation  of  the  observatory,  and  requires  a  cumber- 
some system  of  weights  to  counterpoise  the  shutters  when  they 
go  up  and  down  ;  which  weights  dangle  about  inside  the 
observatory  in  a  way  which  is  exceedingly  inconvenient,  though 
more  or  less  unavoidable.  Besides  these  objections,  this 
system  of  shutter  is  much  more  expensive  to  construct,  and 
not  easy  to  maintain  in  smooth  and  pleasant  working  order, 
to  say  nothing  of  the  difficulty  of  excluding  rain  and  making 
the  place  watertight. 

The  question  of  the  material  for  the  roof  I  have  always  solved 
by  using  |-in.  match-board,  fastened  with  screws,  and  well 
stopped  with  white  lead  and  painted.  When  my  observatory 
was  re-erected  at  Sydenham  in  1908,  after  37  years'  exposure 
to  the  weather,  not  one  single  board  was  found  to  be  in  the 
least  decayed  or  damaged  so  as  to  need  replacement.  Two  or 
three  boards  had  been  cracked  in  taking  them  to  pieces  at 
East  Bourne,  but  these  cracks  were  readily  made  good  by  white 
lead-stopping  and  paint.  In  the  case  of  a  new  roof  constructed 
of  boards  suspected  to  be  insufficiently  seasoned,  it  might  be 
a  good  precaution  to  cover  them  with  canvas,  well  painted  on 
both  sides,  and  fastened  down  with  copper  tacks. 

Willesden  canvas,  sheet  copper,  or  zinc  (without  boards),  may 
also  be  used  for  the  dome.  I  have  heard  Willesden  canvas 
well  spoken  of,  but  have  not  used  it  in  any  position  exposed  to 
the  weather  for  any  length  of  time.  The  copper  or  zinc  may 
be  of  the  ordinary  roofing  thickness,  or  even  thinner.  The 
pieces  must  be  cut  into  sectors  to  fit  the  bays  of  the  dome. 
Each  piece  must  be  secured  at  the  top  and  bottom,  and  on 
cross-battens,  with  copper  or  zinc  nails  ;  but  the  sides  must  be 


I-IGS.  334-337 


PLATE   CXXVI. 


20-ft.  Papier-mache  Dome 
erected  at  the  Royal  Observatory, 
Cape  Town,  with  opening  extend- 
ing beyond  the  Zenith  (Grubb). 


Barcelona  University  (Grubb). 


15-ft.  Papier-mache  Dome, 
mounted  on  iron-framed  Ob- 
servatory covered  with  wood 

(Grubb). 


2781 


Papier-mache  Dome  of  37-ft. 
diameter,  erected  at  Calton  Hill 
Observatory,  Edinburgh  (Grubb), 


FIGS.   338-340 


PLATE    CXXVII. 


o    .1' 


[279 


FURTHER  DETAILS  OF  THE  ROOF.         279 

counter-lapped  (not  soldered)  in  order  to  allow  for  expansion 
by  summer  heat.  Patterns  for  the  sectors  must  be  prepared 
in  brown  paper  after  the  frame  of  the  dome  has  been  put 
together. 

Dome  : 

£    J.     d. 
Contract  price  of  dome,  including  iron  rings  and 

iron  channel-plate        .         .         .         .         .     30     18  II 

Labour :    carpenter    putting    same    together    at 

Sydenham  .         .         .         .         .         .  I     19     8 

32     18     7 


Adding  together  all  the  items  given  previously  under  their 
various  heads  (about  .£69),  it  may  be  taken  that  the  Sydenham 
observatory,  as  it  stands,  represents  a  cost  of,  as  nearly  as 
possible,  ^70,  after  adding  the  value  of  some  etceteras  which 
I  did  not  have  occasion  to  buy  specially.  The  cost  of -repro- 
ducing it  de  novo  might  be  more,  because  of  the  rise  in  the 
price  of  labour  and  materials  since  the  dome  was  constructed 
in  1869  ;  but,  on  the  other  hand,  several  pounds  might  be  saved 
in  the  foundations. 

Thus  far  I  have  been  describing  what  I  have,  more  or  less, 
done  myself,  or  what  has  been  done  under  my  own  direct 
supervision  ;  but  I  am  prepared  to  find  that  many  of  my  present 
readers  will  think  that  my  observatory,  as  it  now  stands  at 
Sydenham,  is  too  solid  ;  in  other  words,  has  been  too  costly 
for  the  purposes  of  amateurs  of  moderate  means  and  ambition, 
though  it  was  far  from  my  intention  to  spend  on  it  more  than 
I  could  help. 

I  fear  there  might  be  some  foundation  for  this  criticism,  and, 
accordingly,  I  would  recommend,  as  an  alternative  to  my  plans, 
a  proposal  which  was  put  forth  nearly  40  years  ago  by  the  late 
Rev.  E.  L.  Berthon,  Vicar  of  Romsey,  the  inventor  of  the  now 
celebrated  "  Berthon  "  boat.  A  description  of  Mr.  Berthon's 
,form  of  observatory,  from  his  own  pen,  appeared  in  The 


280  TELESCOPES. 

English  Mechanic  of  October  13,  1871  ;  and,  as  a  consequence 
of  the  publicity  acquired  in  that  way  and  otherwise,  I  have 
reason  to  believe  that  a  number  of  structures  on  the  Romsey 
model  have  been  erected  in  various  parts  of  the  United 
Kingdom. 

One  such  was  put  up  about  20  years  ago  by  the  late  Mr. 
T.  R.  Clapham,  of  Austwick  Hall,  near  Lancaster,  a  descrip- 
tion of  which,  from  his  own  pen,  appears  in  the  second  volume 
of  my  Handbook  of  Astronomy.  Mr.  Clapham  was  a  clever 
and  ingenious  amateur  mechanic,  and  his  observatory,  which  I 
have  visited,  represented  Mr.  Berthon's  ideas,  with  sundry 
minor  improvements  and  developements  of  an  advantageous 
character  ;  but  I  will  not  go  over  again  the  ground  which 
Mr.  Clapham  kindly  occupied  for  me  in  the  pages  of  the  book 
which  I  have  just  mentioned. 

My  object  in  going  into  the  foregoing  details  hns  been  to 
encourage  my  readers  who  possess  telescopes  which,  though  in 
a  certain  sense  portable,  are  not  readily  portable,  to  make  them 
fixtures,  and  house  them  in  observatories  properly  fitted  up. 
There  can  be  no  question  whatever  that  a  smaller  telescope, 
equatorially  mounted  on  a  fixed  stand,  and  protected  from  the 
weather,  is  capable,  in  careful  hands,  of  yielding  more  useful  and 
profitable  results,  and  in  a  more  pleasant  and  convenient  manner, 
than  a  larger  telescope  mounted  only  on  an  altazimuth  stand 
which  has  to  be  carried  in  and  out  of  a  dwelling-house  on  every 
occasion  that  it  is  used.  It  is  not  always  easy  to  instil  such 
ideas  as  these  into  the  minds  of  junior  astronomers  starting  on 
an  astronomical  career.  To  all  such  I  would  simply  say  that 
I  am  giving  expression  to  the  experience  of  half  a  century 
derived  from  the  ownership  in  succession  of  telescopes  with 
apertures  of  i|  inches  (unmounted),  3  inches  (mounted  on  an 
equatorial  block  without  circles),  4  inches  (mounted  equatorially 
in  an  observatory)  and  6  inches  (ditto).  Perhaps  the  most 
common  mistake  made  by  juniors  of  the  type  which  I  have  now 
in  mind  is  that  of  spending  all  their  available  money  in  increas- 


-Pics.  341-342 


PLATE   CXXVIII. 


Sir  W.  Peek's  Observatory,  Rousden,  Devonshire. 


-  K 


Mr.  J.  Tebbutt's  Observatory,  Windsor,  N.S.W. 


FIG.  343 


PLATE    CXXTX. 


THE    TREPTOW    OBSERVATORY.  28 1 

ing  the  aperture  of  their  instrument,  and  in  regarding  its  stand 
and  its  house  as  minor  matters.  This  is  a  very  grave  mistake, 
especially  in  regard  to  its  stand.  The  use  or  non-use  of  an 
equatorial  mounting,  however  rough,  with  circles  however  coarse 
in  their  graduations,  contrasted  with  an  altazimuth  mounting, 
however  smooth  and  delicately  made,  is  great :  it  means  the 
difference  between  an  hour's  work  in  studying  a  dozen  objects 
with  ease,  or  2  hours'  work  in  hunting  for  and  studying  half  a 
dozen  objects  with  trouble  and  difficulty. 

I  have  met  with  cases  of  persons  owning  equatorials  with 
detachable  telescope-tubes  whose  modus  operandi  is  to  keep 
the  tubes  in  boxes  in  their  houses,  and  have  equatorial  stands 
in  the  open  air  in  their  gardens  covering  up  the  circles,  etc., 
with  boxes  or  waterproof  covers  when  not  in  use,  carrying  the 
tubes  out  of  the  house  and  back  again  as  was  required  ;  but, 
however  unavoidable  in  view  of  particular  circumstances  this 
procedure  may  be,  it  is  not  one  which  will  be  found  conducive 
to  good  work  or  much  work. 

Fig.  344  is  a  view  of  a  telescope  of  entirely  novel  con- 
struction so  far  as  its  mounting  is  concerned,  which  has  been 
erected  near  Berlin  by  an  enterprising  German  astronomer, 
Dr.  Archenhold,  in  spite  of  much  hostile  criticism  on  the  part 
of  German  men  of  science.  The  problem  to  be  solved  was  how 
to  work  a  telescope  of  great  size  and  power  without  the  expense 
and  inconvenience  of  a  very  bulky  and  unhandy  stand  covered 
by  an  enormous  dome  expensive  to  construct  and  laborious  to 
manipulate.  The  difficulty  of  working  giant  telescopes  with 
tubes  50  feet  or  more  long  is  very  great,  especially  when  it  is  a 
question  of  observing  at  one  time  objects  low  down  towards  the 
horizon,  and  at  another  time  objects  overhead  in  the  zenith. 
This  difficulty  nowadays  is  met  in  large  observatories,  con- 
structed regardless  of  expense,  by  surrounding  the  main  pier  of 
an  equatorial  with  a  travelling  floor,  which  can  be  raised  or 
lowered  at  the  pleasure  of  the  observer.  Such  a  system  is 
illustrated  elsewhere  (see  Figs,  338-340,  ante}.  By  means 


282  TELESCOPES. 

of  such  a  floor  the  observer  can  put  his  seat  in  any  position 
which  suits  him,  but  the  time  and  labour  involved  in  bringing 
about  the  necessary  changes  are  very  obvious.  Dr.  Archenhold 
has  been  able  to  arrange  to  keep  the  eye-piece  near  the  centre 
of  motion  by  swinging  the  telescope  tube  in  a  great  fork,  which, 
provided  with  suitable  counterpoises,  permits  of  the  tube  being 
run  up  into  the  air  as  may  be  required,  whilst  the  heavy  mov- 
able parts  are  placed  on  a  solid  concrete  foundation,  which 
secures  due  stability  coupled  with  great  compactness.  In  this 
way  the  working  parts  of  the  mounting  are  housed  under  a 
structure  not  expensive  or  difficult  to  build,  because  of  no  con- 
siderable size,  whilst  the  telescope  tube,  when  not  in  use,  is 
brought  down  into  a  horizontal  position  and  protected  from  the 
weather  by  a  cheap  portable  roof,  which  is  made  to  run  on  it  or 
off  it  as  required.  The  result  of  fitting  up  the  instrument  in 
this  fashion  has  been  to  do  away  with  the  necessity  of  having  a 
large  and  costly  dome  ;  and  the  whole  instrument,  with  its  pro- 
tecting roof,  has  cost  no  more  than  about  ,£13000,  of  which 
,£2300  went  in  the  object-glass,  which  is  said  to  be  an  excellent 
one,  by  Steinheil,  of  Munich,  and  is  27  inches  in  diameter.  It 
will  be  interesting  to  watch  the  future  history  of  this  novel 
construction,  which  was  only  finished  and  brought  into  use  in 
April  1909. 


FIGS.  344-345 


PLATE   CXXX. 


Telescope  at  the  Treptow  Observatory,  Berlin. 


282] 


4-ft.  Reflector  of  the  Melbourne  Observatory, 


FIGS.  346-347 


PLATE   CXXXI. 


28-inch.  Refractor  of  the  Greenwich  Observatory. 

In  use  for  visual  work. 


Meridian  Circle,  U.S.  Naval  Observatory,  Washington. 

[283 


CHAPTER    XV. 
TIME  AND  ITS  MEASUREMENT. 

Years. — Months. — Weeks. — Days. — Hours. — The  Sidereal  year. — The 
Mean  Solar  Year. — The  Anomalistic  Year. — Hipparchus. — The 
Calendar  and  the  reforms  it  has  undergone. — By  Julius  Ccesar. — 
By  Pope  Gregory  XIII. — His  Calendar  adopted  by  England. — 
But  not  by  Russia. — "  Old  Style." — "  New  Style." — The  Lunar 
Month. — The  Week. — Quotation  from  Laplace. — Savages  count 
time  by  "  Moons." — Divisions  of  the  Day. — The  24-hour  Day. — 
a.m.  and  p.m. — Railway  time. — The  "  Prime  Meridian." — 
Greenwich  chosen  for  this. — Standard  time. — Usage  of  different 
Nations. — Where  does  the  dzy  begin  ? — The  Transit  Instrument  and 
how  to  use  it  for  obtaining  the  time. 

"  TEMPUS  FUGIT  "  is  a  truism  which  affects  us  all,  from  babyhood 
to  dotage  ;  but  it  is  a  matter  which,  on  its  historical  side,  has 
many  fascinating  features. 

A  chapter  on  "  Time  and  its  Measurement  "  might  readily 
reach  a  great  length,  but  I  will  put  forward  now  rather  the 
utilitarian  side.  The  subject  will  be  most  conveniently  ap- 
proached by  posing  certain  questions  to  be  used  as  pegs  on 
which  to  hang  such  information  as  it  is  intended  to  give.  Let 
us  start,  then,  with  the  following  questions  : — 

1.  What  is  a  year? 

2.  What  is  a  month  ? 

3.  What  is  a  week  ? 

4.  What  is  a  day  ? 

5.  What  is  an  hour  ? 

6.  Where  does  time  begin  and  end  ? 

7.  How  is  it  measured  ? 

8.  Who  starts  and  runs  the  almanac  ? 


284  TIME   AND    ITS    MEASUREMENT. 

All  these  questions  may  be  said,  at  the  first  glance,  to  have  a 
very  commonplace  appearance,  and  the  solid  science  which  lies 
behind  them  all  is  far  from  being  obvious  ;  nor  do  the  questions, 
when  properly  handled,  admit  of  such  simple  and  easy  answers 
as  might  at  first  sight  appear. 

What  is  a  year  ?  The  answer  is  the  time  occupied  by  the 
Earth  in  performing  one  complete  journey  round  the  Sun,  This 
answer  seems  sufficiently  simple,  but  it  is  not  so  in  reality, 
because  we  have  to  consider  where  the  Earth  starts  from,  and 
where  it  arrives  at  the  end  of  the  interval  which  we  call  the 
"  year."  This  interval,  simpliciter,  is  the  interval  which  elapses 
between  two  successive  passages  of  the  Sun  through  the  same 
equinox,  and  primd  facie  ought  to  be  the  time  which  elapses 
from  the  moment  when  the  Sun  leaves  a  fixed  star  until  it 
returns  to  it  again.  This  kind  of  year  constitutes  the  "sidereal 
year,"  and  in  our  current  notation  consists  of  365  d.  6  h.  9  m. 
It  unfortunately  happens,  however,  that  the  equinoxes  are  not 
fixed  points,  but  are  possessed  of  a  small  retrograde  motion 
from  E.  to  W.,  which  is  constantly  in  progress,  and  the  result 
is  that  the  Sun  gets  round  again  to  the  equinox  from  which 
it  started  before  it  gets  round  to  the  Star  from  which  it  is 
supposed  to  have  started.  The  difference  of  time  is  a  little 
more  than  20  minutes,  so  that  the  year  (which  we  call  the 
"  mean  solar  year  ")  is  20  minutes  shorter  than  the  year  measured 
by  the  stars,  or  sidereal  year.  The  length  of  the  mean  solar 
year  is  therefore  365  d.  5  h.  48m.,  neglecting  fractions,  and  is 
the  year  which  we  talk  about  in  common  conversation  and  in 
almanacs  prepared  for  terrestrial  purposes. 

Besides  this,  astronomers  take  note  of  the  "  anomalistic  year," 
which  is  different  again,  being  365  d.  6h.  13  m.,  and  depends 
upon  the  rather  abstruse  fact  of  the  line  of  apsides  of  the 
Earth's  orbit  beinj*  subject  to  a  progressive  motion  in  virtue 
of  which  the  time  between  the  Earth  passing  one  perihelion 
and  another  differs  from  both  the  mean  solar  year  and  the 
sidereal  year. 


WEEKS   AND   YEARS.  285 

The  month  and  the  week  depend  more  directly  upon  the 
Moon  than  upon  the  Sun  for  their  basis,  as  we  do  not  speak  of 
a  solar  month  or  a  solar  week.  Still,  we  have  the  calendar 
month  of  30  days,  which  is  of  very  ancient  origin,  having  been 
handed  down  to  us  from  a  remote  period  when  the  Sun  was 
assumed  to  pass  through  the  12  signs  of  the  Zodiac  at  an  even 
pace,  with  30  days  allotted  to  each  span  ;  but,  as  this  supposition 
is  at  variance  with  the  fact,  it  was  soon  found  that,  to  treat  the 
year  as  consisting  of  12  months  of  30  days  each,  or  360  days  in 
all,  led  to  such  an  estimate  of  the  year  landing  people  in 
difficulties.  Hence  arose  the  necessity  of  putting  on  an  odd 
period  of  several  days  to  secure  some  sort  of  uniformity  between 
the  movement  of  the  Sun  (or  to  speak  more  correctly,  the 
movement  of  the  Earth  round  the  Sun),  and  the  year  as 
adopted  for  the  purposes  of  civil  reckoning.  When  an  adjust- 
ment of  some  kind  was  first  found  to  be  indispensable  it  began 
with  the  addition  of  5  days  to  the  year,  one  of  which  was  allotted 
to  certain  of  the  12  months.  Then  it  was  discovered,  and  this 
more  than  2000  years  ago,  that  5  days  was  not  enough,  and 
that  it  ought  to  be  5^  days.  Next  it  was  found  that  the  period 
of  5^  days  was  several  minutes  too  much,  and  that  5  h.  55m. 
was  nearer  the  mark.  This  discovery  was  due  to  the  great  Greek 
astronomer,  Hipparchus,  who  flourished  in  the  2nd  century  B.C. 

It  is  in  the  highest  degree  creditable  to  him  that  he  arrived 
at  a  value  so  very  near  the  truth,  for  the  best  modern  results 
show  that  he  was  only  wrong  by  about  6  minutes.  This  state- 
ment does  not  exhaust  the  details  of  this  very  tangled  question. 
Julius  Csesar  was  the  man  who  may  be  said  to  have  started  our 
calendar  nearly  in  its  modern  form.  He  could  not,  of  course, 
take  count  of  fractions  of  a  day,  and  was  obliged  to  assume  that 
the  discrepancy  already  mentioned  was  an  exact  quarter  of  a 
day,  and  would  be  cured  by  dropping  in  a  whole  day  every 
fourth  year. l  The  idea  was  plausible,  and  it  answered  its  pur- 

1  The  bissextile  day=the  second  sextileday,  or  the  6th  day  before  the  Kalends 
of  March  (the  Roman  Notation)  reckoned  twice. 


286  TIME    AND    ITS    MEASUREMENT. 

pose  for  a  long  while,  but  by  the  middle  of  the  i6th  century  things 
had  gone  astray  again,  so  that  the  year  began  10  days  out  of 
place  from  the  day  settled  by  the  Council  of  Nicasa  as  the  ist 
day  of  the  year,  namely  March  21.  This  was  the  origin  of  what 
we  call  the  Gregorian  reform  of  the  calendar,  which  took  its 
name  from  Pope  Gregory  XIII.,  who  brought  it  about  in  1582. 
He  succeeded  in  imposing  his  suggestion  on  the  States  of 
Europe  of  the  Roman  Obedience,  but  the  Protestant  States  and 
the  Greek  Church  did  not  follow  suit.  In  England  the  new 
style  was  not  adopted  till  1752,  when  by  Act  of  Parliament 
1 1  days  were  ordered  to  be  dropped  out  of  the  English  chrono- 
logy at  that  epoch.  This  enactment  caused  a  good  deal  of 
annoyance  and  inconvenience  at  the  time,  and  explains  why  in 
so  many  places  in  English  history  we  find  double  dates,  marked 
O.S.  (old  style)  and  N.S.  (new  style),  and  why  the  national 
financial  year,  which  used  to  end  at  Lady-day,  now  ends  on 
April  5.  Even  to  this  day  the  Greek  Church  sticks  to  the  old 
Julian  calendar,  and  the  discrepancy  between  the  two  styles 
has  grown  to  13  days. 

Various  other  expedients  have  been  propounded,  some  of  them 
of  great  exactness,  for  rendering  more  scientifically  exact  the 
Gregorian  Calendar,  with  its  arrangement  of  leap  years  and  so 
on,  as  we  now  use  it  ;  but,  as  it  is  a  matter  of  adding  or  subtract- 
ing an  extra  day  in  the  course  of  several  thousand  years,  no 
useful  purpose  would  be  served  by  dwelling  on  any  of  these 
proposals  in  this  place. 

The  Lunar  Month  of  28  days,  or  thereabouts,  must  be 
mentioned,  not  that  it  has  any  great  bearing  upon  our  daily 
affairs  except  as  regards  a  calendar  of  the  high  and  low  tides  of 
the  ocean — a  matter  which  comes  home  to  dwellers  on  the  sea- 
coast. 

We  must  now  say  something  about  the  "  week,"  which  is  a 
unit  of  time  of  the  widest  application.  Its  origin  is  lost  in 
antiquity,  and,  though  it  is  usual  to  regard  it  as  the  one-fourth 
portion  of  the  lunar  month,  it  is  impossible  to  doubt  that,  after 


TIME   BY   THE    MOON.  287 

all  said  and  done,  it  is  a  memorial  of  the  creation  of  the 
world,  and  therefore  in  use  for  nearly  6000  years.  Laplace's 
observations  on  this  subject  deserve  to  be  noted  :  "  The  week, 
from  the  very  highest  antiquity,  in  which  its  origin  is  lost,  has, 
without  interruption,  run  on  through  ages  uniting  itself  with  the 
successive  calendars  of  different  nations.  .  .  .  It  is,  perhaps,  the 
most  ancient  and  most  incontestable  monument  of  human 
intelligence,  and  appears  to  indicate  that  all  such  intelligence 
came  from  one  common  source  " — which,  Laplace  might  have 
added,  was  divine.1 

The  part  played  by  the  Moon  in  the  computation  of  time  must 
not  be  too  lightly  esteemed  because,  from  the  earliest  ages  and 
down  even  to  the  present  time  amongst  savage  and  semi- 
civilised  nations,  the  phases  of  the  Moon,  beginning  with  the 
first  appearance  of  the  New  Moon,  furnish  a  chronological  scale 
accessible  to  everybody  and  easily  utilised.  Hence  we  find 
that  savages  often  indicate  considerable  periods  of  time,  which 
we  should  speak  of  as  so  many  months  or  years,  by  saying  that 
such  and  such  a  thing  happened  so  many  "  Moons  "  ago.  This 
meaning,  in  other  words,  that,  since  the  event  in  question 
happened,  they  have  seen  the  Moon  wax  and  wane  so  many 
times.  It  is  easy  to  see  that,  if  a  canoe  was  upset  on  the 
day  that  the  young  Moon  was  first  seen,  and  that  a  young 
Moon  was  seen  again  last  night,  the  interval  is  that  of  one 
"  Moon,"  an  interval  which  might  be  indicated  in  days  if,  since 
the  accident,  every  sunrise  or  sunset  had  been  noted  by  means 
of  a  notch  cut  in  a  stick.  Even  this  method  of  computing 
intervals  of  time  has  been  used  on  occasions  ;  for  instance,  by 
shipwrecked  crews. 

This  brings  us  to  the  next  unit  of  time — the  "  day."  This, 
of  course,  is  in  universal  use  all  over  the  world  by  everybody 
for  every  conceivable  purpose,  but  here  again  the  insoluble 
problem  comes  before  us,  Who  invented  the  idea  of  dividing 

1  Bishop  Christopher  Wordsworth,  in  his  Commentary  on  Genesis,  has  some 
interesting  remarks  which  deserve  attention. 


288  TIME   AND    ITS   MEASUREMENT. 

the  day  into  24  hours,  or  the  alternative  reckoning  of  12  hours 
of  day  and  12  hours  of  night  ?  Here,  again,  are  questions  which 
cannot  be  answered  off-hand,  and  which  in  a  certain  sense  are 
unprofitable  questions.  Hipparchus  seems  to  have  divided  the 
day  into  two  equal  portions  of  12  hours  each,  beginning  one  of 
his  portions  at  midnight  and  the  other  at  noon;  but  it  is  not 
clear  whether  this  was  his  own  original  idea  or  whether  it  was 
borrowed  from  somebody  else.  So  many  systems  were  for- 
merly in  vogue,  alike  as  to  principles  and  details  of  counting 
the  hours,  that  it  would  be  monotonous  to  attempt  to  describe 
them.  Suffice  it  to  say,  generally,  that  whilst  the  total  of  24 
was  in  general  use,  there  have  been  great  varieties  of  prac- 
tice as  to  the  grouping  and  as  to  the  starting-points  of  the 
hours.  While  some  started  from  sunrise,  others  started  from 
sunset.  While  some  started  from  midday,  others  started 
from  midnight.  Others,  again,  ignoring  a  24-hour  division  of 
the  day,  grouped  the  hours  into  triplets  or  quadruplets, 
which  last-named  system  still  prevails  on  board  ship  under  the 
name  of  "  watches." 

Even  the  present  generation  of  inhabitants  of  the  Earth  have 
seen,  or  are  seeing,  some  momentous  changes,  two  in  particular 
which  may  be  said  to  be  not  remotely  connected  with  the  intro- 
duction of  railways.  So  long  as  people  travelled  in  horsed 
vehicles,  or  on  foot,  there  would  never  be  much  confusion 
between  a.m.  (ante-meridian)  and  p.m.  (post-meridian)  because, 
as  a  rule,  in  by-gone  centuries  people  did  not  travel  by  night,  or 
begin  anything  extending  into  the  small  hours  of  the  morning. 
When,  however,  long  main  lines  of  railway,  covering  hundreds 
or  even  thousands  of  miles,  became  available  for  travel,  the 
question  of  time-tables,  and  of  resort  to  them  by  passengers, 
became  serious,  and  the  a.m.'s  and  p.m.'s  of  our  forefathers 
became  very  ensnaring.  The  English  railways,  in  that  conser- 
vative spirit  of  the  nation  which  occasionally  is  not  to  be 
admired,  have  met  the  difficulty  by  various  shifts,  none  of 
which  can  be  pronounced  satisfactory.  Whilst  one  line  uses 


THE    DIVISION    OF   DAYS    INTO    HOURS.  289 

light-faced  figures  for  times  between  6  a.m.  and  6  p.m.,  and 
black  figures  for  the  hours  of  night  between  6  p.m.  and  6  a.m., 
another  line  uses  the  same  sort  of  figures  for  all  hours  and 
contents  itself  with  a.m.  and  p.m.,  and  leaves  it  to  the 
passenger  to  find  his  way  through  the  time-table  as  best  he 
can.  A  third  line,  keeping  to  the  same  sort  of  figures,  indicates 
times  between  noon  and  midnight  by  a  thin  line  between  the 
hour  and  the  minute  figures.  These  expedients  are  all  very 
lame  and  unsatisfactory.  Certain  foreign  nations  have  done 
much  better  by  boldly  taking  the  24  hours  of  the  day  as  the 
only  proper  scale,  and  timing  their  trains  from  o  o'clock  to 
24  o'clock.  Without  doubt  this  is  what,  sooner  or  later,  we 
shall  come  to  in  England,  following,  for  instance,  the  Italians, 
and  more  recently  the  French  (to  some  extent),  who  have  not 
only  adopted  the  24-hour  day  for  railway  purposes,  but  for  every 
purpose. 

The  second  modern  change  in  the  computation  of  time 
alluded  to  above  has  had  reference  to  what  is  called  the 
"prime  meridian,"  or  zero  for  time  on  the  Earth.  Formerly 
every  nation  computed  its  time  from  its  own  capital,  or  some 
such  equivalent  fixed  point  of  longitude.  Thus,  time  in  Great 
Britain  was  reckoned  from  the  Greenwich  meridian  ;  in  Ireland 
from  Dublin  ;  in  France  from  Paris  ;  in  Spain  from  Madrid  ; 
in  Germany  from  Berlin,  and  so  on.  So  that  a  traveller  passing, 
say,  from  Spain  into  Germany,  would  start  with  his  watch 
showing  Madrid  time.  When  he  entered  France  he  would 
have  to  alter  his  watch  from  Madrid  time  to  Paris  time. 
When  he  quitted  the  eastern  frontier  of  France  his  watch, 
regulated  by  Paris  time,  would  be  no  good  for  German  railway 
time-tables;  and  soon.  The  inconveniences  attaching  to  this 
state  of  things  have  probably  been  experienced  by  many 
readers  of  these  pages,  but  they  are  diminishing,  and  in  the 
near  future  will  practically  cease  to  exist  because  the  whole 
world  is  learning  the  advantage  of  having  only  one  prime 
meridian  for  the  whole  world.  By  common  consent,  the 
I9 


2QO  TIME   AND    ITS    MEASUREMENT. 

meridian  of  Greenwich  has  been  selected  as  the  prime  meridian 
of  the  world,  with  provision  for  local  adjustments  to  meet  the 
fact  that  the  Earth  turns  on  its  axis  once  in  24  hours,  and  that 
it  cannot,  therefore,  always  be  noon  or  midnight  at  every  place 
on  the  Earth's  surface  at  the  same  absolute  moment  of  time. 

What  those  adjustments  are  we  have  now  to  consider  in  a 
summary  form,  but,  for  details,  reference  must  be  made  to  such 
publications  as  Whitaker's  Almanac. 

It  has  been  agreed  by  various  nations  that  they  shall  take 
their  time  from  Greenwich  by  differences  of  only  whole  hours, 
so  that  our  ideal  traveller  from  Spain  to  Germany  will  never 
have  to  alter  the  minutes  and  seconds  of  his  watch,  but  only  to 
remember  that  when  he  gets  into  Germany,  or  Austria,  the 
official  hour  will  be  one  hour  in  advance  of  Greenwich  ;  in 
Turkey  and  Egypt  2  hours  in  advance,  and  so  on.  On  the 
other  hand,  when  he  goes  to  America  he  will  find  that  the 
official  hour  at  New  York  is  5  hours  behind  Greenwich,  and  that 
the  time  is  spoken  of  as  "  Eastern  Time,"  the  word  "  eastern  " 
having  reference  to  the  position  of  New  York  with  respect 
to  the  States  of  America.  Further  W.,  as  he  crosses  the 
American  continent,  he  will  come  upon  three  other  "  times  " — 
namely,  "  Central,"  "  Mountain,"  and  "  Pacific "  times,  which 
are  respectively  6,  7,  and  8  hours  behind  Greenwich  time, 
whilst  Eastern  Canada  starts  the  scale  with  "  Atlantic "  time, 
4  hours  slow  of  Greenwich.  This  system  of  nomenclature, 
depending  on  Greenwich,  is  not  limited  to  the  Northern  Hemis- 
phere, because  our  South  African  and  Australasian  Colonies  have 
similarly  adopted  the  Greenwich  meridian.  Some  of  these 
have  split  the  hours  and  taken  the  intermediate  |-hour  as  the 
local  standard  time.  It  will  show  the  comprehensiveness  of 
this  movement  for  standardising  local  times  when  I  state  that 
in  Victoria,  New  South  Wales,  and  Queensland  local  times  are 
linked  to  10  hours  fast  of  Greenwich,  whilst  South  Australia  has 
chosen  9^  hours,  and  New  Zealand  n^  hours  fast  of  Greenwich 
for  their  respective  bases. 


TIME   ALL   OVER   THE   WORLD. 


291 


The  annexed  diagram,  which  is  published  ihere  by  the  kind- 
ness of  the  Society  for  the  Propagation  of  the  Gospel,  though  it 


'2NIDWCMT   II30P* 

Fig.  348.— Time  all  over  the  world  (by  permission  of 
the  S.P.G.). 


is  not  actually  graduated  according  to  the  official  nomenclature 
dependent  on  hours  in  advance  of  or  behind  the  Greenwich 
meridian,  will  yet  serve  the  useful  purpose  of  informing 


292  TIME   AND    ITS    MEASUREMENT. 

readers  what  are    the    local    times  relatively  to  Greenwich  of 
the  countries  which  are  named. 

The  meridian  of  Greenwich  runs  through  France  and  North- 
West  Africa,  and  at  Accra,  on  the  Gold  Coast,  there  is  a  certain 
house  of  which  it  is  said  that  the  Greenwich  meridian  cuts 
through  it  exactly  to  within  r^tfth  of  a  second.  The  writer  of 
the  article  in  the  S.P.G.  magazine  from  which  this  diagram 
is  borrowed  playfully  remarks  that  : — 

"There  is  one  place  in  the  world,  in  the  middle  of  the 
Pacific  Ocean,  where  the  time  seems  to  go  all  wrong.  The 
Editor  was  once  crossing  from  New  Zealand  to  South  America, 
when,  on  Sunday  evening,  as  he  had  finished  holding  services 
for  the  passengers,  the  captain  passed  word  round  the  ship  that 
the  next  day  would  also  be  Sunday,  the  same  day  of  the  month. 
He  did  not,  however,  hold  any  more  services,  but  the  week  of 
which  this  day  was  the  beginning  had  8  days  in  it.  As  a  storm 
continued  during  the  whole  time,  it  seemed  a  very  long  week." 

This  allusion  to  what  always  happens  when  a  ship  passes  the 
iSoth  meridian  from  Greenwich,  deserves  some  elucidation,  and 
I  am-able  to  present  the  converse  of  what  has  just  been  narrated. 

Mr.  C.  O.  Burge,  a  retired  Civil  Engineer,  writes  : — 

"  Just  before  arriving  in  New  Zealand  we  had  to  cross  the 
meridian  180°  West  and  East,  the  antipodes  of  longitude,  and,  in 
order  to  keep  time  with  the  world's  almanac,  had  to  lose  a 
day — that  is  to  say,  to  go  directly  from  Saturday  to  Monday  ; 
but,  as  the  captain's  birthday  would  have  been  on  the  missing 
Sunday,  and  it  would  have  been  lost  if,  to  use  an  expression 
appropriate  to  my  nationality,  the  omission  had  been  celebrated 
on  the  Sunday,  it  was  decided  to  leave  out  Saturday  instead. 
All  of  us,  therefore,  who  did  not  return  in  the  reverse  direction 
lost  a  day  never  to  be  recovered,  unless  in  the  little  pieces  of 
the  extended  days  of  our  return  to  the  old  country,  possibly 
years  later,  while  those  who  remained  in  the  Antipodes  never 
got  it  back  at  all.  For  us,  there  were  only  364  days  in  that 
year,  a  sort  of  true  Leap  Year,  for  we  jumped  over  a  day — a 
missing 

"'  Syllable  of  recorded  time.' 


WHEN    THE    DAY    BEGINS.  293 

"  In  the  case  of  voyages  in  the  opposite  direction — that  is  to 
say,  eastwards  across  this  meridian — an  extra  day  must  be 
interpolated  to  keep  time  with  the  world.  It  is  said  that  an 
Irishman,  which  he  wasn't  at  all,  as  he  would  say,  being  born 
on  the  ocean,  was  launched  into  this  sea  of  troubles  on  the 
day  following  the  29th  February  of  a  Leap  Year  when  the  ship 
in  which  his  mother  was  a  passenger  was  crossing  the  180° 
meridian  eastwards.  His  natal  day  was  therefore  the  inter- 
polated 30th  of  February,  which  for  him  never  occurred  again. 
So,  though  he  lived  to  a  great  age,  he  never  had  a  subsequent 
birthday."  ' 

This  chapter  may  include  the  asking  of,  and  the  trying  to 
answer,  a  very  tricky  question,  "  Where  does  any  given  day, 
say,  New  Year's  Day,  begin  ? "  The  most  definite  answer 
which  can  be  given  seems  to  be  this— that,  in  the  case  of  all 
nations  which  use  maps  which  have  the  longitude  of  Greenwich 
as  their  zero  longitude,  their  day  must  be  regarded  as  com- 
mencing at  the  longitude  of  180°  E.,  and  that  accordingly  as 
one  starts  from  that  longitude  and  works  westwards,  so  the  day 
begins,  place  by  place,  on  the  surface  of  the  Earth  as  the  E. 
longitude  diminishes  from  180°  down  to  no  longitude  at  all, 
which  is  therefore  Greenwich  itself. 

As  the  i Both  degree  of  E.  longitude  passes  through  a  point 
in  the  Northern  Hemisphere  in  Eastern  Siberia,  and  in  the 
Southern  Hemisphere  slightly  to  the  E.  of  New  Zealand, 
therefore  in  a  certain  paradoxical,  or  imaginary,  sense  the  day 
for  people  in  the  Northern  Hemisphere,  whose  longitude 
standard  is  Greenwich,  may  be  said  to  depend  on  Eastern 
Siberia 2  as  the  place  where  their  day  begins,  whilst  people  in 
the  Southern  Hemisphere  under  corresponding  circumstances 
may  be  said  to  have  their  day  start  from  near  the  eastern 
coast  of  New  Zealand. 

1  C.  O.  Burge,  Adventures  of  a  Civil  Engineer,  p.  244.     London,  1909. 

2  This  is  only  true  in  theory,  because  practically  the  line  of  demarcation  is 
treated  as  passing  through  Behring's  Straits,  and  all  Siberia  as  having  East 
longitude  for  lime  purposes. 


294  TIME    AND    ITS    MEASUREMENT. 

The  foregoing  pages  may  suffice  for  furnishing  some  ele- 
mentary ideas  on  the  general  principles  which  underlie  the 
measurement  of  time  from  the  standpoint  of  one  who  regards 
the  matter  in  its  immediate  bearings  on  the  daily  affairs  of 
life  ;  but  a  good  deal  more  would  have  to  be  said  before  the 
subject  of  "  Time "  could  be  deemed  at  all  exhausted.  It 
would  be  necessary  to  tell  the  reader  how  the  astronomical 
facts  which  control  our  measurement  of  time  are  brought  down 
from  the  heavens  on  to  the  surface  of  the  Earth,  and  how 
everything  is  tabulated  to  form  the  basis,  first  of  our  calendar, 
and  then  of  our  almanacs — but  all  these  things  would  take  us 
too  far  afield  from  the  main  purpose  of  the  present  volume. 

In  the  chapter  on  the  telescope  *  I  have  named  all  the 
equipment  necessary  for  the  ordinary  purposes  of  an  amateur 
observer ;  but  if  he  wishes  to  go  beyond  the  mere  telescope 
and  the  clock,  and  the  building  to  house  both,  there  is  one 
accessory  instrument  which  he  will  find  very  useful,  namely, 
the  transit  instrument  for  keeping  his  clock  correct  without 
the  necessity  of  bringing  the  time  home  by  his  watch  every 
few  days,  and  then  having  in  each  case  to  convert  the  civil 
mean  time  into  sidereal  time. 

The  principle  of  the  transit  instrument  is  very  simple,  and 
the  practical  use  of  it  is  not  at  all  difficult  or  troublesome  ;  so 
much  so  that  in  remote  country  districts,  away  from  towns  and 
railway-stations,  one  occasionally  comes  upon  a  non-scientific 
country  gentleman  who,  making  no  professions  of  astronomy, 
has  and  uses  a  transit  instrument  of  some  sort  for  mere  time- 
keeping purposes. 

The  principle  of  the  instrument  is  this :  that  every  star  crosses 
the  meridian  of  a  given  place  at  a  definite  time,  as  laid  down 
in  the  Natitical  Almanac  ;  and,  if  instrumental  means  are 
at  command  for  determining  the  exact  moment  when  a  star 
crosses  the  meridian,  and  a  Nautical  Almanac  (or  some 
sufficient  substitute)  is  also  at  command,  the  time  is  imme- 
1  Chapter  XIV.,  ante. 


THE   TRANSIT    INSTRUMENT. 


295 


diately  obtainable, 
upon  the  pre- 
cision of  the 
instrument  used 
and  the  care 
which  is  exer- 
cised. Accord- 
ingly a  large 
and  carefully 
adjusted  transit 
instrument  will 
give  a  more 
accurate  result 
than  one  which 
is  small  and 
only  roughly 
adjusted.  And 
such  an  instru- 
ment will  give 
a  better  result 
than  no  instru- 
ment at  all,  for 
the  time  of 
the  meridian 
passage  of  a 
star  can  be 
ascertained  by 
such  a  thing  as 
a  wall  running 
truly  N.  and  S., 
the  arrival  of 
the  star  coming 
up  from  the 
E.  in  the  line 
of  the  wall 


The  accuracy  of  the  result  will  depend 


Fig.  349.— The  Transit  Instrument  for 
obtaining  the  time. 


296  TIME    AND    ITS    MEASUREMENT. 

being  noted   by  a  clock,   or   even   a  watch  with   a   seconds 
hand. 

In  all  such  cases  the  principle  is  simply  this  :  the  almanac 
says  that  the  star  ought  to  arrive  at  the  meridian  at  a  certain 
instant  marked  by  the  time  expressed  in  hours,  minutes,  and 
seconds.  If  the  star  arrives  seemingly  too  soon  the  clock 
or  the  watch  is  too  slow.  If  the  star  should  arrive  after  its 
appointed  time  the  clock  or  watch  is  too  fast.  In  carrying 
out  observations  such  as  those  just  described  the  observer  will 
have  to  convert  sidereal  time  into  mean  solar  time  in  order 
to  find  when  the  star  ought  to  appear  ;  and  he  will  also  have 
to  convert  mean  solar  time  into  sidereal  time  when  he  wants 
to  know  what  hour  of  R.A.  is  on  the  meridian  at  a  given 
moment. 

The  ordinary  small  or  "  Portable  Transit  Instrument  "  ex- 
ternally consists  of  3  principal  parts,  which  will  be  understood 
without  difficulty  by  looking  at  the  illustration  (Fig.  349).  There 
are  (i)  the. telescope  ;  (2)  the  stand  on  which  it  is  mounted  ;  and 
(3)  the  declination  circl^.  The  telescope  tube  is  made  in  2 
parts,  which  are  connected  by  a  centre-piece,  a  cube  in  shape. 
Into  the  centre-piece,  at  right  angles  to  the  main  tube,  are 
fitted  2  branch  tubes  usually  conical,  which  together  form  the 
horizontal  axis  of  the  telescope.  The  smaller  ends  of  these 
transverse  tubes  are  accurately  ground  to  form  2  perfectly 
equal  cylinders  or  pivots.  These  pivots  rest  on  Y's,  which  are 
angular  bearings  surmounting  the  side-standards  which  support 
the  instrument  as  a  whole.  One  of  the  Y's  is  fixed  in  a 
horizontal  groove,  so  that  by  means  of  a  screw  a  small  azi- 
muthal  motion  may  be  imparted  to  the  tubes  as  a  whole  which 
constitute  the  upper  portion  of  the  instrument.  The  vertical 
screws  which  go  through  the  base  are  available  for  raising 
or  lowering  the  entire  instrument  so  as  to  make  sure  that  the 
bearings  which  rest  in  the  Y's  shall  be  truly  horizontal. 

At  one  end  of  the  horizontal  axis  a  graduated  circle  is  fixed, 
which  is  to  be  so  adjusted  that  the  telescope  can  be  set  to 


THE    USE    OF    THE   TRANSIT   INSTRUMENT. 


297 


stars  of  any  given  declination.  This  circle  is  divided  into 
degrees  and  subdivisions  of  a  degree  to  be  read,  when  great 
exactness  is  required,  by  means  of  a  Verneer.  At  the  opposite 
end  of  the  horizontal  axis  provision  is  made  to  receive  light 
coming  from  a  lamp,  and  designed  to  illuminate  the  wires 
which  are  fixed  in  the  eye-piece  of  the  telescope.  This  light 
from  the  lamp,  when  it  reaches  the  centre-piece,  is  reflected 
up  the  telescope  to  the  eye-piece  by  means  of  a  diagonal 
reflector  fixed  in  the  tube.  A  movable  striding  level  runs 
across  from  standard  to  standard 
to  be  used  to  ensure  the  hori- 
zontality  of  the  horizontal  axis. 
The  lamp  may  or  may  not  be 
furnished  with  a  sliding  dia- 
phragm to  admit  much  or  little 
light  according  as  the  star  to  be 
observed  is  a  bright  one,  or  a 
small  one  likely  to  be  overcome 
if  too  much  light  is  admitted. 

Assuming  that  the  transit 
instrument,  so  far  as  its  special 
features  have  already  been  ds- 
scribed,  is  in  good  workmg 
order,  the  climax  of  its  success 
depends  upon  the  wires  which 

appear  in  the  field  of  view  when  the  instrument  is  open  for  use 
(Fig.  350).  Literally  only  one  vertical  wire  is  required,  because, 
supposing  the  instrument  is  in  proper  adjustment  when  the 
telescope  is  moved  up  and  down,  that  one  vertical  wire  travels 
in  the  meridian  of  the  place  of  observation.  It  is,  however, 
found  in  practice  that  an  observer  watching  a  star  crossing 
one  wire  is  more  likely  to  make  a  trifling  mistake  in  estimating 
the  right  moment  by  the  clock  than  if  he  notes  clock-time  at 
5  wires  and  strikes  an  average.  It  is  usual,  therefore,  to 
provide  $  vertical  wires,  the  calculation  of  an  average  from 


359.—  The  Planet  Venus 
an(j  a  star  as  seen  in  a 
Transit  Instrument. 


298  TIME    AND    ITS    MEASUREMENT. 

which  is  easy.  While  it  must  be  stated  that  3  wires  are  better 
than  i,  but  not  so  good  as  5,  yet  7  are  better  than  either  3  or 
5,  and  are  provided  in  the  large  Transit  Circles  used  in  the 
great  public  observatories. 

There  is  in  every  transit  instrument  one  horizontal  wire 
which  serves  to  subdivide  the  field  of  view  horizontally,  and  to 
indicate  the  place  where  the  star  may  be  expected  to  cross 
the  field  if  the  declination  circle  has  been  properly  adjusted 
to  the  tabular  declination  of  the  star ;  but  the  horizontal  wire 
has  no  direct  connection  with  the  results  yielded  as  regards  the 
time.  It  need  hardly  be  stated  that  the  accuracy  of  the  ulti- 
mate result  depends  upon  the  instrument  as  a  whole  being 
accurately  adjusted  to  its  work,  and  this  means  that  when 
moved  up  and  down  it  should  always  be  in  the  meridian  ;  that 
the  horizontal  axis  should  be  truly  level  ;  that  the  wires  and 
the  object  should  both  be  in  focus  at  the  same  time  ;  that  the 
centre  wire  should  be  exactly  in  the  optical  axis  of  the  tele- 
scope ;  and  that  the  main  tube  should  be  truly  at  right  angles 
to  the  horizontal  axis.  All  these  requirements  are  obtained  by 
means  of  suitable  adjustment  screws,  which  need  not  be  more 
particularly  described  here.1 

Fig.  351  is  intended  to  represent  graphically  a  thing  which 
is  not  very  generally  understood — the  "  Equation  of  Time  "  : 
what  it  is,  and  why  it  should  exist,  or  be  required  to  be  acted 
upon.  The  explanation  is  really  very  simple.  We  talk  roughly 
of  the  day  as  an  interval  of  time  depending  on  the  Sun  crossing 
the  meridian  every  day,  or  really  on  the  rotation  of  the  Earth 
on  its  axis — and  such  is  the  case,  broadly  stated  ;  but  the  day 
which  depends  on  the  Sun  differs  from  and  is  longer  than  the 
sidereal  day  by  an  amount  (3m.  56  s.)  which,  though  trifling, 
will  disturb  the  even  course  of  events  unless  adjusted  somehow, 
and  the  equation  of  time,  as  it  is  called,  supplies  the  means  of 
adjustment.  The  fons  et  origo  of  the  whole  inconvenience  is 

1  See  for  such  details  my  Handbook  of  Astronomy,  vol.  ii.,  "  Astronomical 
Instruments,"  and  other  books  of  the  like  nature. 


THE    EQUATION    OF    TIME.  299 

the  fact  that  the  Earth's  orbit  not  being  a  circle,  but  an  ellipse, 
the  Earth's  pace  in  moving  round  the  Sun  (or  the  apparent 
daily  motion  of  the  Sun  through  the  zodiac)  is  not  uniform,  but 
is  faster  with  the  Sun  in  perigee  in  January  than  it  is  with  the 
Sun  in  apogee  in  July.  Hence  it  follows  that,  to  keep  an  even 
day  of  24  hours  throughout  the  year  (the  "  mean  solar  day  "), 
we  must  equalise  in  some  way  the  irregular  length  of  the 


Fig.  351.— Diagram  to  represent  graphically  the 
Equation  of  Time. 

apparent  solar  day,  and  the  Equation  of  Time  is  the  expedient 
adopted. 

I  have  never  seen  the  actual  circumstances  involved  in  the 
measurement  of  time  and  the  differences  of  time  resulting  from 
the  Earth's  rotation  on  its  axis  so  graphically  expressed  as  they 
have  been  by  Mr.  E.  W.  Maunder  in  an  obscure  but  very 
excellent  monthly  penny  magazine  called  The  Cottager,  pub- 
lished by  the  Religious  Tract  Society.  The  whole  article  is 


30O  TIME    AND    ITS    MEASUREMENT. 

worth  reading,  but  the  particular  passage  which  I  wish  to 
assimilate  will  make  the  idea  sufficiently  clear.  The  ideal 
observer  is  supposed  to  have  gone  up  in  a  balloon  from  a  place 
in  East  London,  near  the  East  India  Dock  Gates,  and  to  have 
risen  say  500  ft. — somewhat  higher  than  the  cross  of  St.  Paul's. 
The  writer  then  proceeds  as  follows  : — 

"Taking  a  watch  in  our  hand,  we  will  note  what  happens. 
As  we  look  out,  we  see  all  London  below  us.  To  the  E.  it  does 
not  stretch  very  far,  but  we  can  trace  it  on  both  sides  of  the 
winding  Thames  out  to  Barking  and  Woolwich.  N.  and  S.  it 
stretches  farther  ;  W.  we  cannot  see  distinctly  where  it  ends. 

"  It  is  not  the  great  city  itself,  however,  to  which  I  wish  to 
draw  your  attention,  but  to  the  fact  that  it  is  all  on  the  move. 
It  is  slipping  away  from  under  us,  ten  times  faster  than  any 
express  train  in  which  we  ever  rode.  We  started  from  the 
Dock  Gates — our  watch  has  only  beat  6  seconds— and  the  great 
tower  of  Limehouse  Church  has  rushed  by.  We  see  St.  Paul's 
hurrying  to  us  ;  in  12  seconds  more  the  Tower  passes  us  on 
the  left,  and  6  seconds  later  the  great  Cathedral  has  reached  us. 

"  Four  seconds  more  bring  the  Law  Courts  beneath  our  feet  ; 
another  12  seconds  and  it  is  the  Marble  Arch.  It  takes  only  7 
seconds  for  Hyde  Park  and  Kensington  Gardens  to  glide  by  ; 
and  Shepherd's  Bush,  Acton,  and  Ealing  are  sweeping  forward 
towards  us.  In  I  minute  from  the  time  that  we  rose  up  at  the 
Dock  Gates  the  mighty  city  has  gone  by.  Another  minute 
takes  us  out  of  Middlesex,  and  in  10  minutes  from  our  start  we 
pass  Bristol.  If  we  had  tried  to  reach  it  by  the  Great  Western 
Railway  we  should  have  required  2^  hours  for  the  journey." 


CHAPTER   XVI. 
THE   SPECTROSCOPE  ASTRONOMICALLY. 

What  is  a  spectrum  ? — The  decomposition  of  sunlight. — Brief  history 
of  the  application  of  prisms  to  sunhght. — Labours  of  Grimaldi. — 
Of  Sir  I.  Newton. — Of  Wollaston. — Of  Fraunhofer. — The  lines  in 
the  spectrum  named  by  him. — And  after  him. — Some  details  as  to 
these. — Their  interpretation. — The  labours  of  Huggins  and  others. 
— Application  of  the  spectroscope  to  celestial  objects. — Secchi's  star 
types. — Motions  of  the  stars  as  ascertained  by  the  spectroscope. 

A  SPECTROSCOPE  is,  of  course,  from  its  very  name,1  an  instru- 
ment for  examining  a  spectrum,  and  therefore  we  must  begin 
at  the  beginning,  and  learn  what  a  spectrum  is,  and  how  an 
instrument  for  examining  it  is  constructed.  But  before  getting 
as  far  as  this  it  will  be  desirable  to  give  a  little  historical 
retrospect. 

The  celebrated  Italian  astronomer  and  ecclesiastic,  Antonio 
Secchi,  S  J.,  once  remarked  that  it  might  almost  be  said  that, 
in  offering  to  us  the  brilliant  colours  of  the  rainbow,  the 
Creator  has  in  effect  invited  us  to  examine  the  composition  of 
light  and  to  study  its  nature.  This  mystery,  however,  was  not 
revealed  to  us  until  a  comparatively  recent  period.  The 
"  triangular  glass  "  (as  the  prism  was  once  called)  has  long 
been  known  :  its  power  to  colour  the  rudest  objects,  and  to 
transform  them  into  a  cluster  of  precious  stones,  was  a  source 
of  amusement  for  the  world  in  general,  though  a  matter  deemed 
little  worthy  of  the  notice  of  the  philosopher. 

1  Spectrum,  and  a-Koireui,  I  view. 
301 


302  THE   SPECTROSCOPE   ASTRONOMICALLY. 

A  certain  Grimaldi  was  one  of  the  first  to  study  the  prism 
scientifically,  and  he  did  so  with  much  care  and  success.  He 
made  a  hole  in  the  shutter  of  a  darkened  room,  through  which 
he  let  in  a  ray  of  sunlight,  which  he  submitted  to  the  action  of 
his  prism.  He  was  thus  enabled  to  break  up  his  ray  of  light, 
which  came  from  the  Sun,  and  so  obtain  the  solar  spectrum, 
which  in  due  course  he  carefully  described.  After  this  experi- 
ment, he  proceeded  to  transmit  rays  of  sunlight  through  glass 
spheres  filled  with  water.  This  enabled  him  to  propound  an 
explanation  of  the  rainbow,  which  was  subsequently  worked 
out  by  Newton.  Grimaldi's  modus  operandi,  reproduced  pic- 
torially,  was  the  basis  of  all  those  engravings,  showing  how  a 
ray  of  simple  white  light  is  split  up  into  colours,  which  are 
found  in  every  book  ever  written  on  the  subject. 

It  seems  hardly  necessary  to  dwell  on  the  details  of  this, 
though  perhaps  I  had  better  do  so.  The  ray  of  light  entering 
a  room  through  the  hole  in  the  shutter  meets  the  prism, 
and,  passing  through  it,  comes  out  on  the  opposite  side, 
not  as  a  single  ray,  as  it  entered,  but  split  or  decomposed 
(to  use  the  technical  term).  When  it  reaches  the  screen 
it  has  become  a  wide  strip  of  coloured  light,  red  at  one 
end  and  violet  at  the  other,  with  many  intermediate  shades 
of  colour  in  between.  Newton  repeated  the  experiment 
in  consequence  of  information  derived  from  Grimaldi,  and 
so  far  improved  upon  it  as  to  point  out  that  passing  the 
spectrum  through  a  second  prism  did  not  cause  any  further 
change.  He  communicated  his  supplementary  discovery  to 
his  friend  Arland,  of  Geneva,  in  a  rough  pen-and-ink  sketch, 
to  which  he  prefixed  the  important  legend,  "  Nee  variat 
lux  fracta  colorem "  (The  decomposed  light  undergoes  no 
change). 

This  impossibility  of  decomposing  any  further  a  ray  which 
has  already  traversed  one  prism  constitutes  in  reality  the 
discovery  made  by  Newton  ;  but  he  got  a  step  beyond  this,  for 
he  recomposed  white  light  out  of  colours  by  determining  the 


SPECTRUM    ANALYSIS    HISTORICALLY.  303 

proportions  in  which  it  was  necessary  to  do  this  in  order  to 
reproduce  a  light  analogous  to  that  of  the  Sun.  He  also 
assigned  names  to  the  different  colours. 

A  long  interval  of  time  elapsed  after  Newton  before  any 
substantial  progress  was  made  in  this  department  of  Optics. 
Wollaston  was  the  next  man.  In  looking  at  a  narrow  slit  of 
sunlight  through  a  prism,  he  saw  that  the  spectrum,  instead  of 
being  continuous,  showed  gaps  in  the  form  of  black  streaks, 
which  divided  the  spectrum  into  many  compartments.  This 
discovery  attracted  no  attention,  and  remained  without  fruit 
until  Fraiinhofer,  wishing  to  determine  more  exactly  the  index 
of  refraction  of  certain  sorts  of  glass  which  he  was  using, 
perceived,  and,  so  to  speak,  rediscovered  what  Wollaston  had 
previously  discovered.  He  contrived  methods  of  studying  these 
streaks,  sketched  them,  and  eventually  defined  their  positions 
relatively  to  one  another  by  direct  measurement.  In  conse- 
quence of  his  industrious  labours,  the  black  streaks  or  lines 
just  alluded  to  are  universally  known  nowadays  as  "  Fraiin- 
hofer's  Lines,"  though  priority  for  their  discovery  rests  dis- 
tinctly with  Wollaston. 

There  is  no  great  difficulty  in  seeing  these  lines.  It  is 
necessary  to  look  directly  at  the  slit,  and  to  focus  the  eye-piece 
of  a  telescope  of  sorts  on  to  the  slit,  so  as  to  see  the  slit  very 
clearly  defined.  Then,  after  having  placed  the  prism  in  the 
path  of  the  luminous  rays,  and  in  the  position  which  answers 
to  that  of  minimum  deviation,  the  telescope  must  be  brought 
to  bear  on  the  prism,  and  when  the  eye-piece  is  again  duly 
adjusted,  by  being  brought  to  a  focus,  the  lines  will  be  visible. 
If  the  prisrn  is  a  good  one,  and  the  telescope  is  achromatic,  a 
great  number  of  very  fine  lines  will  be  seen. 

Fraiinhofer  applied  to  the  principal  lines  observed  by  himself 
certain  letters  of  the  alphabet ;  capitals  for  some,  and  small 
letters  for  others.  These  leading  lines  must  be  looked  for  as 
follows  :  A  in  the  extreme  red  ;  B  in  the  moderate  red  ;  C  in 
the  reddish- orange  ;  D  in  the  yellow-orange  ;  E  and  b  in  the 


304  THE    SPECTROSCOPE   ASTRONOMICALLY. 

green  ;  F  at  the  commencement  of  the  blue  ;  G  in  the  indigo  ; 
H  in  the  violet.  These  standard  letters,  as  they  may  be  called, 
are  in  universal  use,  but  subsidiary  letters  have  been  introduced 
since  Fraiinhofer's  time,  and  also  certain  figures  for  facilitating 
the  comparison  of  the  different  parts  of  the  solar  spectrum  with 
the  recognised  table  of  wave-lengths.  The  caution  may,  per- 
haps, well  be  given  here  that  the  lines  do  not  correspond  with 
what  might  be  regarded  as  the  boundaries  of  the  colours  of  the 
spectrum,  but  are  wholly  independent  of  them. 

These  letters  being  understood  generally,  some  details  may 
well  now  be  given  which  will  make  their  use  as  an  index  to  the 
solar  spectrum  better  appreciated.  A  is  a  strong  line  close  to 
the  red  end  of  the  spectrum.  B  is  a  strong  and  rather  broad 
line  i  in  the  red  near  its  middle.  Between  A  and  B  is  a  group 
of  several  lines  collectively  called  a.  C  is  a  dark  and  well- 
marked  line  where  the  red  is  passing  into  orange.  Between 
B  and  C  Fraiinhofer  counted  9  fine  lines  ;  between  C  and  D 
he  counted  about  30.  D,  in  the  orange,  where  it  is  passing  into 
yellow,  consists  of  2  strong  lines  close  together.  Between  D 
and  E  Fraiinhofer  counted  84  lines.  E,  in  the  yellowish-green, 
is  a  compound  band  of  several  lines,  the  middle  one  of  which 
is  stronger  than  the  rest.  At  b  there  are  3  strong  lines,  the 
2  farthest  from  E  being  close  together.  Between  E  and  b 
Fraiinhofer  counted  24  lines,  and  between  b  and  F  more  than 
50.  The  lines  F,  G,  and  H,  which  are  at  the  commencement 
of  the  blue,  in  the  indigo,  and  in  the  violet  respectively, 
are  well  defined.  Between  F  and  G  Fraiinhofer  counted 
185  lines,  between  G  and  H  190  lines,  and  many  lines  beyond 
Hand  between  H  and  I  at  the  extreme  violet  end  of  the 
spectrum. 

It  will  readily  be  realised  that  these  dark  lines  are  gaps  or 
breaks  in  the  spectrum,  but  it  will  not  be  so  easily  realised  why 
there  should  be  these  gaps,  indicative,  as  they  are,  primarily,  of 
the  absence  of  rays  of  certain  refrangibilities  from  the  beam  of 
sunlight  which  we  are  supposed  to  be  describing.  It  is  obvious 


SPECTRUM    ANALYSIS    GENERALLY.  30^ 

that  something  lies  behind  the  absence  of  so  many  intermediate 
rays  of  light,  narrow  though  they  be,  and  slight  as  may  be  the 
joint  effect  they  may  have  on  the  spectrum  of  the  Sun  on  a 
cursory  inspection  of  it. 

The  story  of  the  history  of  the  successive  stages  in  which 
knowledge  gradually  accumulated  in  the  interpretation  of  these 
mysteries  is  far  too  long  to  be  told  here,  but  the  substance 
of  it  is  this  :  that  various  metals  and  earths  in  a  state  of 
incandescence  or  combustion,  when  examined  through  the 
prisms  of  a  spectroscope,  yield  certain  bright  lines,  and 
that  in  many  cases  the  distribution  of  these  bright  lines  is 
coincident  with  the  presence  of  dark  lines  in  the  spectrum  of 
sunlight. 

When  some  of  these  spectra  are  carefully  compared  with  the 
lines  in  the  spectrum  of  the  Sun,  and  the  coincidence  of  bright 
lines  of  known  origin  with  dark  lines  of  unknown  origin  is 
established,  the  inference  is  drawn  (through  stages  of  proof 
which  I  do  not  detail)  that  the  absence  of  light  where  the  dark 
lines  appear  is  due  to  the  presence  in  the  Sun  of  a  substance 
identical  in  nature  with  a  substance  which  is  on  the  Earth,  and 
is,  when  examined,  found  to  yield  the  particular  bright  lines 
just  spoken  of,  and  no  other  bright  lines. 

The  example  usually  cited  to  illustrate  this  is  that  of  sodium. 
Formerly  no  interpretation  could  be  given  of  the  D  lines  in  the 
solar  spectrum.  At  a  later  stage  in  the  progress  of  experiments 
it  was  found  that,  when  sodium  (or  its  equivalent,  common 
salt)  was  burnt  in  the  flame  of  a  spirit-lamp,  there  was  pre- 
sented in  the  spectroscope  no  other  prominent  lines,  bright  or 
dark,  than  the  double  D  line.  Hence  physicists  came  to  the 
conclusion  that  sodium  in  the  form  of  vapour  was  one  of  the 
substances  which  is  burning  perpetually  in  the  Sun.  I  must 
cut  a  long  story  short  by  saying  that  many  researches  and 
experiments  by  various  eminent  men  at  various  dates  and  at 
various  places  have  led  to  the  inference  that  a  large  number 
of  jnetals  and  mineral  substances  known  on  the  Earth  exist 

20 


306  THE   SPECTROSCOPE   ASTRONOMICALLY. 

on  the  Sun,  and,  by  suitable  treatment  by  means  of  spectro- 
scopes, can  be  individualised.  On  the  other  hand,  there  are 
lines  in  the  solar  spectrum  which  cannot  be  interpreted  except 
on  the  assumption  that  there  are  the  Sun  substances  absent  from 
the  Earth,  and  physicists  have  felt  themselves  justified  in 
individualising  some  of  these,  and  giving  them  newly  invented 
names,  such  as  helium  and  coronium. 

In  the  first  instance,  and  during  all  the  early  years  of  the  use 
of  the  spectroscope  astronomically,  its  application  was  chiefly 
to  the  Sun,  and,  though  Fraiinhofer  carried  out  some  experi- 
ments on  certain  conspicuous  stars,  it  cannot  be  said  that  the 
method  of  spectrum  analysis  was  applied  on  any  considerable 
scale  in  other  astronomical  fields  than  the  Sun  until  Muggins, 
in  1864,  began  his  famous  researches  into  the  constitution  of 
planets,  comets,  clusters,  and  nebulae. 

Thus  far  general  principles.  The  next  matter  which  should 
receive  attention  is  the  construction  in  practice  of  spectro- 
scopes for  actual  use  in  the  study  of,  not  simply  the  Sun, 
but  any  and  all  celestial  objects.  This,  however,  is  a  large 
subject,  altogether  beyond  the  scope  of  this  elementary 
volume. 

And,  indeed,  the  subject  of  astronomical  spectroscopy  itself 
is  far  too  vast  to  be  brought  in  at  the  tail-end  of  a  popular  book 
on  general  astronomy,  and  is,  moreover,  a  study  not  likely  to 
be  taken  up  by  the  readers  for  whom  this  volume  is  more 
especially  designed.  I  shall  therefore  conclude  by  alluding 
to  two  topics  which  may  perhaps  induce  a  few  of  my  readers 
to  wish  to  go  a  step  further  by  the  aid  of  books  specially 
dedicated  to  spectroscopic  astronomy. 

The  first  matter  to  be  mentioned  is  Secchi's  classification 
of  stars.  Whilst  Huggins,  working  in  conjunction  with  his 
friend,  Dr.  W.  A.  Miller,  of  King's  College,  examined  some- 
thing like  loo  stars  spectroscopically,  Secchi  investigated  the 
spectra  of  about  500  stars,  and  was  led  to  distribute  them 
into  4  classes  or  types,  an  account  of  which  he  published 


307 


308  THE    SPECTROSCOPE    ASTRONOMICALLY. 

in    1868.      Secchi's    types    may    be     briefly    summarised    as 
follows  : — 

1.  White  stars,  of  which  Sirius  and  Vega  are  types,  yielding 
spectra  crossed  by  4  broad  dark  lines,  due  to  hydrogen,  much 
broader  than  those  in  the  solar  spectrum.     Sodium  and  mag- 
nesium may  be  easily  identified  in  such  stars. 

2.  Yellow  stars,  such  as  Aldebaran,  Capella,  Pollux,  Arcturus, 
and  a  Cygni,  wherein  the  hydrogen  lines  are  much  less  con- 
spicuous   than    in    Type    I.,   but    metallic    lines,   magnesium 
especially,  are  numerous. 

3.  Stars  with  exceedingly  beautiful  spectra,  crossed  by  10  or 
more  dark  bands,  each  band  very  dark  and  sharp  on  the  violet 
side,    and   gradually   growing   fainter    towards    the    red   end. 
Betelgeuse  (a  Orionis),  a  Herculis,  and  Antares  (a  Scorpii),  are 
the  principal  stars  of  this  type. 

4.  Red  stars,  which  show  3  broad  dark  bands,  shaded  in  the 
reverse  direction  to  those  of  the  3rd  type. 

These  4  types  of  stellar  spectra  are  generally  recognised  by 
astronomers,  though,  after  Secchi,  far  more  numerous  observa- 
tions, carried  out  by  Vogel,  Duner,  Lockyer,  and  others,  led  to 
other  classifications.  However,  Secchi's  4  types  have  not  been 
generally  superseded,  though  it  ought  to  be  added  that  he 
himself  was  inclined  to  constitute  a  5th  class  of  stars  showing 
bright  lines  in  their  spectra. 

The  following  points  may  be  stated  summarily. 

The  following  stars  have  banded  spectra  : — a  Orionis  ;  o  Ceti  ; 
a  Herculis  ;  p  Ursa  majoris  ;  /3  Andromeda  ;  a  Tauri  ;  /3  Pegasi  ; 
a  Scorpii  ;  y  Crucis.  Stars  of  the  helium  type  are  mainly  dis- 
tributed in  the  galactic  zones  ;  Orion  stars  are  mainly  of  the 
helium  type  ;  Sirian  stars  of  the  hydrogen  type  ;  Procyon  stars 
of  the  calcium  type. 

The  last  matter  in  connection  with  stellar  spectroscopy, 
which  must  just  be  named,  is  Huggins's  interesting  and  in- 
genious application  of  the  spectroscope  to  isolated  stars,  with 
the  view  of  determining  their  velocities  of  approach  and 


SPECTRUM    ANALYSIS   APPLIED    PRACTICALLY.  309 

recession  in  the  line  of  sight  to  and  from  the  Sun.  Though 
the  whole  idea  of  such  an  attempt  to  prove  stellar  movement 
by  means  of  the  spectroscope  seems  a  high  flight  of  imagina- 
tion, yet  it  does  not  appear  that  there  are  sufficient  grounds  for 
distrusting  the  results  arrived  at  in  the  case  of  several  dozen 
stars,  though  these  results  require  us  to  talk  about  miles  per 
second  as  the  pace  at  which  the  stars  in  question  are  travelling 
to  and  from  somewhere. 


CHAPTER   XVII. 


TABLE  OF  THE  CONSTELLATIONS,  WITH 
A  BRIEF  DESCRIPTIVE  ACCOUNT  OF 
EACH. 

BY  the  entries  in  the  column  headed  "  Centre  "  it  is  meant  to 
be  inferred  that  a  line  of  Right  Ascension  and  a  line  of  Declina- 
tion taken  off  the  map  will  intercept  at  a  point  which  may  be 
regarded  as  about  the  centre  of  the  constellation.  This,  how- 
ever, is  only  true  of  the  more  compact  constellations,  for  there 
are  some,  like  Draco,  Cetus,  and  Argo,  which  are  so  long  and 
straggling  that  they  extend  over  several  hours  of  R.A.  When, 
therefore,  I  state  that  the  constellations  are  here  arranged  in 
the  order  of  R.A. ,  the  statement  must  be  regarded  as  needing 
some  qualification  in  many  cases.  In  the  column  of  "  Declina- 
tion "  +  means  North,  and  —  South. 


Name  of  Constellation. 

Centre. 

R.A. 

Dec  I. 

Pisces     

Sculptor  (Apparatus  sculptoris)     .         .         . 
Andromeda  ....... 
Phcenix  .         .         .         .         .                  , 

h.  m. 
O  2O 

o  30 

o  40 

I      0 
I      0 

*  45 

2      O 
2    25 
2    30 
2    40 

3  20 

+     10 

+  38 
-  48 

+   60 

—     12 
+    32 

-  33 

+     20 
-     72 
+    42 

Cassiopeia 

Cetus     

Triangulum    ....... 

Fornax  (Chenrica)  ...... 
Aries     
Hydrus  

Perseus  

310 


THK   POSITION    OF   THE    CONSTELLATIONS. 


Name  of  Constellation. 

Centre. 

R.A. 

Decl. 

h.  m. 

3  20 
3  So 
3  So 
4  3° 
4  40 
5    o 
5  20 
5  25 
5  30 
5  40 
5  40 
5  40 
6    o 
6  40 
7    o 
7    o 
7  30 
7  40 
7  So 
8    o 
830 
8  40 
8  40 
9    o 
9  30 
10    o 

10    10 

10  20 
10  30 
10  40 

II      0 
II      0 
II    20 
12    20 
12    30 
12    30 
12   40 
13      0 
13   20 

0 

-     52 
-    63 
-     30 
+     18 
-     42 
-    60 

+     3 
—  20 

-  52 
-  77 
-  34 
+   70 
+  42 
_  24 
-f-   24 
-     3 
+     6 
-  32 
+   45 
_  40 

+     20 
_    62 
-    69 
-    30 

-  45 
-  35 
—     i 

+   33 
+    15 
-  78 

—     12 

+     58 
-    15 
-    60 

-   18 
-  68 

+   27 
+   40 
-  47 

Reticulum  (Rhomboidalis)     .... 

Taurus  .         .         .         .         ;    '     .    "     .         . 
Cselum  (Ccela  sculpt  oris)        .         .         . 

Orion     .        ....         *  '      .... 
Lepus    .         .         .         .         * 
Pictor  (Equleus  pictoris)         .         . 
Mensa  (Mons  tnensa)     .         .         .         .         . 

Camelopardus        .         ....     .   . 
Auriga  
Canis  Major  *. 
Gemini  
Monoceros     

Argo(/VAO        

Argo      
Cancer  ........ 
Argo  (Carina)       

Argo  (Ma/us)        
Argo  (  Vela]  

Sextans          
Leo  Minor     
Leo        
Chamseleon    
Hydra   
Ursa  Major   
Crater    
Crux      .         .         .         .         .                  . 
Corvux  x 
Musca  Australis     
Coma  Berenices     
Canes  Venatici       
Centaurus      

312 


CONSTELLATIONS. 


Centre. 

TU^                   r/-«            4     ii_».' 

R.A. 

Decl. 

h.  m. 

o 

Virgo     

13   2O 

—       2 

Bootes  

14  35 

+     3O 

Circinus          

14  50 

Lupus    

15    o 

-     40 

Libra     

15  10 

.-     14 

Apus      ........ 

15  3° 

-    76 

Serpens          ....... 

15  35 

+  '    8 

Corona  Borealis     

15  4° 

+   30 

Triangulum  Australe      ..... 

15  40 

-  65 

Ursa  Minor   

15  40 

-t-   7& 

Norma  ........ 

16    o 

-   49 

Draco    

16    o 

+    60 

Scorpio  

16  20 

_   26 

Ara        

16  50 

-  55 

Ophiuchus     
Hercules         ....... 

17  10 
17  10 

-     4 
+   27 

Corona  Australis    

18  30 

Scutum  Sobieskii  

18  30 

_     10 

Telescopium  

18  40 

-  52 

"  Lyra      

18  45 

+   36 

Sagittarius     

19    o 

-  25 

Pavo              .... 

19  10 

2  ** 

Aquila  (with  Antinoiis)          .... 

19  30 

-.       2 

Sagitta  
Vulpecula  et  Anser         ..... 

19  50 

20  10 

+    18 
+   -5 

Cygnus  
Delphinus      ....... 

20    30 

20  35 

-r    40 
+     12 

Capricornus  

20   50 

_    20 

Microscopium         

21      O 

-   37 

21    IO 

+     6 

Indus     

21    2O 

-  58 

Piscis  Australis      .         .         .         . 

21    40 

-  32 

Cepheus         

22      0 

4-     70 

Grus      , 

22    2O 

-  47 

Aquarius        

22   20 

-   13 

22    25 

T    43 

Pegasus          

22   30 

T"O 

+     17 

Toucan  .         .        .  .  "      .         .         .         .         . 

23  45 

-  68 

Polar 

(South) 

CONSTELLATIONS:  R.A.,  OH.  OM.  TO  2  H.  25  M.     313 

A  few  lines  will  now  be  given  to  each  of  these  constella- 
tions by  way  of  assisting  an  observer  in  finding  them  and  in 
recognising  their  constituent  stars.1 

Pisces  (The  Fishes)  is  a  dull  and  uninteresting  constellation, 
the  precise  whereabouts  of  which  can  only  be  discovered  by 
glancing  upon  it  from  neighbouring  constellations.  It  immedi- 
ately adjoins,  to  the  S.,  the  "  Square  of  Pegasus,"  by  means  of 
which,  therefore,  it  can  be  readily  found.  The  2  brightest  stars 
are  77  and  y,  each  about  mag.  3! , 

Sculptor  is  a  southern  constellation,  barely  visible  in  England. 
Its  brightest  star,  a,  is  only  of  mag.  4. 

Andromeda  ("The  Chained  Lady")  is  one  of  the  largest  and 
most  important  constellations  in  the  northern  heavens,  contain- 
ing as  it  does  3  stars  of  the  2nd  mag.  (a,  /3,  y),  whilst  8  is  3^, 
and  v  and  o  are  both  3f. 

Phoenix,  a  southern  constellation,  has  the  following  bright 
stars  :  a  2^,  /3  and  y  both  3^,  and  c  3f. 

Cassiopeia  ("The  Lady  in  her  Chair")  is  a  constellation  of  great 
extent  and  of  much  interest  to  the  telescopist,  owing  to  the  fact 
that  a  part  of  the  Milky  Way,  very  rich  in  stars,  runs  through  it. 
Its  naked-eye  stars  include  the  well-known  W.  group.  The 
chief  stars  are  :  a  2,  y  and  /3  2|,  8  2|,  and  77,  e,  £,  all  about  3^. 

Cetus  (The  Whale)  is  a  very  large  constellation  as  regards  its 
area,  but  of  no  great  interest  from  a  naked-eye  or  telescopic 
point  of  view.  Its  most  interesting  object  is  the  celebrated 
variable  star  Mira.  The  chief  stars  are  :  /3  2,  a  2|,  t,  77,  r,  andy, 
all  3i,  and  6,  f,  „,  all  3|. 

Trianguhim  (The  Triangle).  This  is  one  of  the  ancient 
constellations,  notwithstanding  its  small  size.  Its  principal  stars 
are  /3  3,  and  a  3^. 

Fornax  Chemica  (The  Chemical  Furnace).     In  speaking  of 

1  The  more  exact  valuations  now  in  use  take  account  of  differences  of 
magnitude  amongst  the  larger  stars  to  tenths.  These  refinements  are, 
however,  ignored  in  the  paragraphs  which  follow,  and  the  magnitudes  are 
given  only  to  quarters  of  a  magnitude. 


314     CONSTELLATIONS:  R.A.,  2  H.  30  M.  TO  5  H.  OM. 

this  constellation  it  is  usual  to  drop  the  word  "  Chemica."     It 
has  no  brighter  star  than  one  of  mag.  4^. 

Aries  (The  Ram).  In  the  Ram's  head  there  are  3  moderately 
conspicuous  stars  which  serve  to  indicate  the  position  of  the 
constellation.  These  are  :  a  2,  j3  2|,  and  y  4. 

Hydrus  (The  Small  Snake).  This  is  a  southern  constellation 
not  far  from  the  S.  Pole.  Principal  stars  :  /3  2|,  and  a  and  y, 
both  about  3. 

Perseus.  This  is  a  very  brilliant  constellation,  because  it 
embraces  a  very  rich  portion  of  the  Milky  Way.  Its  chief  stars 
are  :  a  2,  /3  2j,  f,  y,  £,  6,  all  about  3,  and  p,  3! .  /3  Persei,  better 
known  by  its  Arabic  name  of  "Algol,"  is  a  very  remarkable 
variable  star  of  short  period. 

Horologium  (The  Clock),  a  southern  constellation,  has  one 
fairly  conspicuous  star,  a  3|. 

Reticulum  (The  Net)  is  also  a  southern  constellation.  Chief 
stars  :  a  3^,  and  /3  4. 

Eridanus  is  a  very  long,  straggling  constellation,  reaching 
from  the  Equator  to  60°  of  S.  Declination.  Its  important  stars 
are  invisible  in  England.  They  are  :  a  (Achernar)  I  ;  #,  2^  ; 
/3  andy,  3  ;  v4  and  $,  3^  ;  together  with  e,  d,  Flamsteed's  12,  v7  and 
r4,  all  about  3! . 

Taurus  (The  Bull).  This  is  a  large  and  interesting  constella- 
tion comprising  naked-eye  and  telescopic  objects  in  great 
variety.  Amongst  the  former  are  the  celebrated  groups  of  the 
Pleiades  and  the  Hyades  and  the  beautiful  ist-magnitude  star 
Aldebaran.  The  other  bright  stars  are  :  182,  »?,  £,  3,  X,  0J,  3^ ; 
together  with  e,  o,  £,  and  Flamsteed's  17  and  27,  all  of  about  3f. 
Besides  these  there  are  no  fewer  than  48  stars  ranging  from 
mag.  4  to  5J. 

Caluni  (The  Graving  Tool)  is  a  small  southern  constellation, 
the  two  brightest  stars  of  which,  a  and  y,  are  only  4^. 

Dorado  (The  Sword-fish),  a  southern  constellation,  has  for  its 
chief  stars  :  a  3,  and  /3  4.  This  constellation  contains  a  cele- 
brated cluster  of  stars. 


FIG.  353. 


PLATE  CXXXII. 


Central  Portion  of  Orion  (F.  W.  Longbottom). 


314] 


FIGS.  354-355 


PLATE  CXXXIII. 


[315 


CONSTELLATIONS:    R.A.,    5  H.    2O  M.    TO    7  H.    O  M.       315 

Orion,  This,  though  not  in  area  the  largest,  is  by  far  the 
most  brilliant  and  interesting  of  all  the  constellations,  both  as 
regards  its  naked-eye  stars  and  its  telescopic  objects.  Its 
position,  too,  is  very  good  for  observers  in  England,  as  it  comes 
to  the  meridian  in  the  winter  at  a  very  convenient  altitude.  Its 
2  brightest  stars,  /3  (Rigel)  and  a  (Betelgeuse),  are  both,  especi- 
ally the  former,  brighter  than  the  average  ist-magnitude  stars  ; 
then,  besides,  there  are  4  of  the  2nd  magnitude,  *,  -y,  £,  K.  Next 
follow  d  2^,  i  3,  vr1  3j,  77,  X,  r,  3^,  and  a-  3!,  with  45  stars  of  mags. 
4  to  Si 

Lepus  (The  Hare)  is  a  small  constellation  immediately  S.  of 
Orion,  with  the  following  conspicuous  stars  :  a  2|,  /3  3,  €  and  /M  3^, 
and  C,  17,  y,  3f  • 

'  Pictor  (The  Painter)  is  a  southern  constellation  with  the 
following  as  its  chief  stars  :  a  3^,  /3  4. 

J/0/Z.T  Mensa  (The  Table  Mountain),  in  the  Southern  Hemi- 
sphere, is  one  of  the  least  important  of  all  the  accepted  constella- 
tions, and  has  no  star  brighter  than  5^. 

Columba  Noachi  (Noah's  Dove),  generally  called  Columba,  is 
a  small  constellation  to  the  S.  of  Lepus,  and  only  partly  visible 
in  England.  Its  chief  stars  are  :  a  2  j,  /3  3,  and  e  3!. 

Camdopardus  (The  Camelopard)  is  a  long,  straggling  con- 
stellation with  a  large  number  of  4th-magnitude  stars,  but 
nothing  brighter. 

Auriga  (The  Charioteer)  is  a  constellation  occupying  a  large 
area,  and  with  one  star  in  particular,  a  (Capella),  which  is  very 
brilliant,  being  indeed  in  the  judgment  of  some  the  second 
brightest  star  visible  in  England,  ranking  after  Sirius.  The 
other  bright  stars  are  :  |3,  2  ;  0,  i,  2|  ;  e,  77,  3!  ;  and  5,  3! . 

Cants  Major  (The  Greater  Dog).  This,  though  quite  a  small 
constellation  as  regards  its  area,  contains  a  large  number  of 
conspicuous  stars,  including  the  brightest  of  all,  Sirius.  The 
other  bright  stars  are  :  e  i£,  S  if,  |8  2,  77  2^,  £,  o3,  3,  and 
Flamsteed's  22  and  28,  both  about  3^. 

Bernini  (The  Twins)  has   2   stars  with  familiar  names   as 


316     CONSTELLATIONS:  R.A.,  7  H.  o  M.  IOH.  TO  o  M. 

leaders,  together  with  several  others  of  lesser  magnitude.  The 
chief  stars  are  :  /3  (Pollux)  i,  a  (Castor)  i£,  y  2,  /u,  and  e  3^,  £,  s,  X, 
5  and  K  all  about  3^,  and  6  3f. 

Monoceros  (The  Unicorn)  has  2  stars  of  mag.  4  and  nothing 
larger ;  it  is,  however,  not  an  unimportant  constellation,  being 
rich  in  telescopic  objects  owing  to  its  position  in  the  Milky  Way. 

Cants  Minor  (The  Lesser  Dog),  though  a  small  constellation, 
will  always  be  readily  found  by  its  a  (Procyon),  one  of  the 
largest  of  the  ist-magnitude  stars.  The  next  star,  /3,  is  only  of 
mag.  3. 

Argo  (The  Ship  Argo)  is  not  an  easy  constellation  to  describe 
because  of  its  great  extent,  and,  by  way  of  facilitating  work  in 
its  confines,  it  has  been  by  common  consent  cut  up  into  4 
divisions,  respectively  called  Carina  (The  Keel),  Mains  (The 
Mast),  Puppis  (The  Poop),  and  Vela  (The  Sails),  to  which  some 
add  a  5th,  Pyxis  Nautica,  a  part  of  Malus.  The  conspicuous 
stars  are  :  a  (Canopus),  a  very  bright  ist-mag.  ;  then  follow 
ft  *,  8,  2  ;  i,  £,  X,  2£  ;  K,  $,  2|  ;  <9,  p,  p,  y,  3  ;  r,  v,  3  J  ;  £,  i>,  <r,  o>,  3^  ; 
X^  V')  3l-  These  stars  will  be  found  scattered  all  over  the 
constellation.  Canopus  is  the  second  brightest  star  in  the 
heavens,  being  but  slightly  inferior  to  Sirius,  which  it  only 
precedes  in  R.A.  by  about  18  m. 

Lynx  is  a  troublesome  constellation  to  find,  its  brightest  star, 
a,  being  only  3^  ;  and  the  next  one.  Flamsteed's  38,  only  3! . 

Cancer  (The  Crab).  The  most  conspicuous  star  is  j3,  only  3^  ; 
but  the  cluster  "  Praesepe  "  will  indicate  this  constellation  to  the 
naked-eye  observer. 

Volans.  The  proper  name  of  this  southern  constellation  is 
Piscis  Volans  (The  Flying  Fish)  ;  but,  as  there  are  2  other  Fishes 
in  the  heavens  (Pisces,  the  Zodiacal  constellation,  and  Piscis 
Australis),  it  has  been  agreed  to  drop  the  3rd  Piscis  and 
use  only  the  word  "  Volans."  Its  chief  stars  are  :  y  and  /3, 
both  about  3|. 

Antlia  Pneumatica  (The  Air-pump).  The  brightest  star  is  a 
only  of  mag.  4^. 


FIG.  356 


PLATE   CXXXIV. 


The  "  Southern  Cross.' 


516] 


FIG.  357 


PLATE   CXXXV. 


The  Spiral  Nebula,  51  M.  Canum  Venaticorum  (Earl  of  Rosse). 


[317 


CONSTELLATIONS:    R.A.,    IO  H.    TO  M.    TO    12  H.    2O  M.    317 

Sextans  (The  Sextant)  is  an  insignificant  constellation,  and  its 
brightest  star  only  45. 

Leo  Minor  (The  Lesser  Lion)  lies  to  the  N.  of  Leo  Major  ; 
its  brightest  star  is  Flamsteed's  46,  of  mag.  4. 

Leo  (The  Lion).  The  prominent  feature  of  this  constellation  is 
the  group  of  stars  known  as  "  The  Sickle."  The  chief  stars  are  : 
a  (Regulus),  i£  ;  v,  0,  2\  ;  8,  2f  ;  e,  3  ;  0,  77,  f,  all  3^  ;  and  o,  3^ . 

Chamceleon.  This  is  a  small  and  unimportant  constellation 
not  far  from  the  S.  Pole,  and  with  no  star  brighter  than  a,  4^. 

Hydra  (The  Water-snake).  A  long-straggling  constellation 
extending  through  more  dian  6  hours  of  R.A.  Chief  stars  : 
a,  2  ;  £,  v,  y,  TT,  e,  all  about  3 J. 

Ursa  Major  (The  Great  Bear).  This  has  already  been  some- 
what fully  described  on  a  previous  page.  Its  chief  stars  are  : 
€  (Alioth),  i|  ;  a  (Dubhe)  and  77  (Benetnasch),  both  2 ;  £ 
(Mizar),  /3  and  y,  all  2j  ;  /*,  ^,  t,  0,  all  3  ;  o,  e,  X,  3^  ;  *,  ^,  |,  i/,  3|. 

Crater  (The  Cup)  is  a  small  constellation  sometimes  treated 
as  part  of  Hydra.  Its  2  principal  stars  are  :  Flamsteed's  19, 
and  8,  both  of  them  scarcely  of  mag.  4. 

Crux  (The  Cross).  This  is  a  southern  constellation,  small  in 
size,  but  with  4  conspicuous  stars  which  suggested  its  name. 
Opinions  seem  much  divided  as  to  whether  it  really  is  a  striking- 
group.  The  chief  stars  are  :  a  ij,  /3  if,  y  2,  and  8  3^.  The  fol- 
lowing is  the  opinion  of  Mr.  W.  B.  Gibbs,  F.R.A.S.  : — 

"The  Southern  Cross"  is  formed  by  five  stars,  of  which  only 
one  is  of  the  ist  magnitude,  the  others  are  of  the  2nd  and  lower 
magnitudes.  Closely  following,  a  few  degrees  away,  are  the  two 
bright  stars  a  and  3  Centauri,  which  are  sometimes  called  "  The 
Pointers."  When  the  cross  is  vertical  its  longer  diagonal  points 
to  the  S.,  and  at  any  other  time  the  South  Pole  may  be  approxi- 
mately found  by  prolonging  this  diagonal  4^  times  its  own  length 
in  the  direction  of  the  South  Pole.  Altogether  these  two  stars 
of  the  Centaur  and  those  of  the  Southern  Cross  make  a  most 
notable  group,  the  most  characteristic  star-group  of  the  Southern 
Hemisphere." 


318  CONSTELLATIONS:  R.A.,  12  H.  30  M.  TO  15  H.  TOM. 

Corvus  (The  Crow).  A  small  constellation  with  some  very 
bright  stars,  several  of  which  are  suspected  to  be  variable. 
The  4  chief  stars,  y  and  )3,  both  2f,  and  e  and  8  both  3,  form  a 
trapezium. 

Musca  Australis  (The  Southern  Fly)  is  a  southern  constella- 
tion. Chief  stars  :  n  3,  /3  3^,  5  and  B.A.C.  3984,  both  3|. 

Coma  Berenices  (Berenice's  Tresses)  is  a  small  constellation 
of  medium-sized  stars  distributed  at  somewhat  even  intervals. 
The  brightest,  /3,  is  only  4^,  but  there  are  17  as  bright  or 
brighter  than  5^. 

Canes  Venatici  (The  Hunting  Dogs).  This  constellation  has 
but  one  bright  star,  a,  called  also  "  Cor  Caroli."  Hevelius 
desired  to  form  this  into  a  separate  constellation  to  commemo- 
rate Charles  II. 

Centaurus  (The  Centaur)  is  a  large  and  important  southern 
constellation  with  many  bright  stars,  none  of  which  are  visible 
in  England.  These  are  :  a2,  /3,  both  of  mag.  I  ;  6  if  ;  y,  77,  e, 
2i  5  C,  8,  2f  ;  i,  3  ;  K,  3!  ;  X,  /z,  a1,  3^,  and  v,  3! . 

Virgo  (the  Virgin)  has  one  very  bright  star,  a  (Spica),  but 
is  a  constellation  chiefly  noted  for  its  many  nebulae.  The 
other  chief  stars  are  :  f,  e,  3  ;  £,  3^  ;  /3,  6,  Flamsteed's  109, 
all  3l; 

Bootes  (The  Bear  Leader).  This  is  one  of  the  largest  of  the 
northern  constellations,  and  possesses  in  a  (Arcturus)  one  of 
the  most  brilliant  of  the  northern  stars,  its  rivals  being  a  Aurigas, 
and  a  Lyrae.  Its  other  chief  stars  are  :  e,  i\  ;  77,  y,  3  ;  8,  /3,  p, 

3*;C,3l. 

Circinus  (The  Compasses)  is  a  very  small  southern  con- 
stellation, the  brightest  star  of  which  is  a,  3^. 

Lupus  (The  Wolf)  is  a  southern  constellation,  a  mere  frag- 
ment of  which  is  visible  in  England.  The  bright  stars  are  : 
«,  3,  2| ;  y,  3 ;  £  01,  3^  ;  8,  *,  77,  t,  all  3^. 

Libra  (The  Balance)  is  so  low  down  in  the  southern  horizon 
that  it  is  not  easy  to  get  hold  of  it,  especially  as  its  visibility 
coincides  with  the  short  nights  of  the  English  summer.  Its 


CONSTELLATIONS:  R.A.,  15  H.  30  M.  TO  i6n.  50  M.  319 

principal  stars  are  :  /3,  2f,  and  a  and  Flamsteed's  20,  both 
about  3. 

Apus{  (sometimes  called  Avis  Indica,  The  Bird  of  Paradise) 
is  a  small  constellation  not  far  from  the  South  Pole,  and  its 
brightest  star,  a,  is  only  about  mag.  4. 

Serpens  (The  Serpent)  is  a  straggling  constellation,  much 
mixed  up  with  Ophiuchus.  The  chief  stars  are  :  a,  2f  ;  77,  p.,  3^  ; 
and  e,  |,  £,  all  about  3^. 

Corona  Borealis  (The  Northern  Crown)  bears  more  resem- 
blance to  its  name  than  most  of  the  constellations  do.  Chief 
stars  :  a,  2^,  and  /3,  3!  ;  with  13  stars  between  4  and  55-. 

Triangulum  Australe  (The  Southern  Triangle)  is  a  small 
southern  constellation,  with  several  bright  stars  :  a,  2|,  and  y,  /5, 
each  3. 

Ursa  Minor  (The  Little  Bear)  is  often  spoken  of  as  being  a 
facsimile  of  the  Great  Bear,  but  the  idea  is  rather  far-fetched. 
The  real  importance  of  this  constellation  is  due  to  the  Northern 
Polar  point  and  the  Pole  Star  being  within  its  boundaries.  Its 
chief  stars  are  :  /3  (Kochab),  and  a  (Polaris),  both  about  2  ;  and 

y,3i 

Norma  (The  Rule)  is  an  unimportant  southern  constellation, 
whose  brightest  star  (y2)  is  only  of  mag.  4^. 

Draco  (The  Dragon)  is  a  constellation  which  may  almost  be 
said  to  extend  everywhere,  for  it  reaches  through  nearly  12  hours 
of  R.A.,  and  is  circumpolar  in  England.  The  difficulties  of 
studying  it  are  aggravated  by  the  fact  that  when  on  the  meridian 
it  is  absolutely  in  the  zenith.  Chief  stars  :  y,  2^  ;  77,  2| ;  /3,  3  ; 
C,  3i  5  i,  «,  3?  5  X,  *>  3l  5  with  43  stars  ranging  from  4  to  5^. 

Scorpio  (The  Scorpion)  is  a  zodiacal  constellation,  rather  un- 
favourably placed  for  observers  in  England.  Its  principal  star, 
a,  of  mag.  i,  is  known  as  Antares  (  =  the  "rival  of  Mars"),  a 
name  given  to  mark  its  red  colour.  The  other  chief  stars  are  : 
X,  if ;  (9,  f,  2  ;  S,  K,  2±  ;  v,  2| ;  /31,  r,  o-,  TT,  all  3  ;  tl,  3^  ;  ^,  £2,  77, 
all  3i 

Ara  (The  Altar)  is  a  small  constellation,  but  with  a  good 


320  CONSTELLATIONS:  R.A.,   17  H.   IOM.  TO  19  H,  50  M. 

share  of  medium-sized  stars.     These  are  :  ft  2|  ;  a,  3  ;  £,  3^  ;  y, 
32  J  ^  *?>  3l  J  #>  «S  D0tn  about  4. 

Ophiuchus^  sometimes  called  Serpentarius  (The  Serpent- 
bearer),  is  much  mixed  up  with  Serpens,  the  animal  carried, 
and  with  Hercules.  The  chief  stars  are  :  a,  2| ;  ?/,  2^  ;  S,  £,  2| ; 
ft  3  ;  e,  K,  0,  i/,  all  about  3^  ;  y  and  Flamsteed's  72,  both  3|. 

Hercules  is  a  large  and  important  constellation,  with  a  great 
variety  both  of  naked-eye  and  of  telescopic  objects.  Its 
principal  stars  ars  :  ft  2!  ;  £,  3  ;  a,  8,  3^  ;  TT,  /n,  3!  ;  77,  y,  3!;  with 
41  stars  from  4  to  55. 

Corona  Australia  (The  Southern  Crown)  is  a  southern  con- 
stellation with  no  stars  brighter  than  mag.  4.  It  is  to  be 
noticed  that  6  of  its  naked-eye  stars  are  disposed  in  a  curved 
line. 

Scutum  Sobieskii  is  sometimes  called  Clypeus  Sobieskii,  but 
the  single  word  Scutum  (The  Shield)  is  its  more  usual  designa- 
tion. Its  brightest  star  is  B.A.C.  6325  of  mag.  4. 

Telescopium  (The  Telescope)  is  a  small  southern  constellation, 
the  brightest  star  of  which  is  a,  3^. 

Lyra  (The  Lyre)  is  a  constellation  small  in  size,  but  it  pos- 
sesses in  its  a  (Vega)  a  very  brilliant  ist-magnitude  star,  and 
a  great  variety  of  important  telescopic  objects.  After  Vega 
come  y,  3^  ;  and  ft  3^. 

Sagittarius  (the  Archer),  by  reason  of  its  low  altitude  in 
England,  is  not  generally  appreciated,  but  it  contains  a  con- 
siderable number  of  important  stars.  Thus  :  e,  2  ;  er,  2^  ;  8,  2-f  ; 
C,  />  >7,  \  TT,  all  3  ;  0,  3[ ;  £3,  r,  3^ ;  /31,  3!  ;  with  36  stars  from 
4  to  51 

/W0  (The  Peacock)  is  a  small  southern  constellation  with 
some  conspicuous  stars  :  a,  2  ;  ft  3^  ;  8,  3^  ;  77,  3! . 

Aquila  (The  Eagle),  though  only  a  small  constellation,  is  rich 
in  bright  and  double  stars.  The  chief  stars  are  :  a,  i  ;  y,  2|  ; 
£,  3  ;  6,  8,  X,  3^  ;  whilst  ?;,  is  a  bright  4. 

Sagitta  (The  Arrow)  is  a  small  but  ancient  constellation,  with 
2  stars,  y,  8,  both  of  them  about  3^. 


CONSTELLATIONS,    R.A.,    2O  H.    IOM.    TO    22  H.     2O  M.       32! 


?cula  et  Anser.  As  a  fox  and  a  goose  were  2  things 
which  formerly  were  supposed  to  go  together  (for  a  short  time), 
so  Vulpecula  had  an  Anser  associated  with  him  ;  but  the  Anser 
has  long  since  disappeared  down  the  Fox's  throat,  and  as- 
tronomers only  talk  now  of  the  Fox.  The  brightest  star  is  a,  4^  ; 
but  there  are  no  fewer  than  14  stars  ranging  from  4|  to  5^. 

Cygnus  (The  Swan)  is  a  large  and  important  constellation, 
with  much  in  it  to  interest  all  classes  of  students.  A  rich  part 
of  the  Milky  Way  occupies  a  considerable  area  of  it,  and  a 
large  number  of  prominent  red  stars  are  also  among  its  special 
features.  The  chief  stars  are  :  a  (Deneb)  i^  ;  y,  2|  ;  c,  2f  ;  d,  j3 
(Albireo),  3  ;  £,  3^ ;  £,  to',  3! ;  together  with  no  fewer  than  53 
stars  between  4  and  5^. 

Delphinus  (The  Dolphin)  is  an  unimportant  northern  constella- 
tion, the  brightest  star  of  which  is  ft  3! . 

Capricornus  (The  Goat)  is  a  constellation  low  down  in  Eng- 
land, with  not  much  to  attract  the  naked  eye.  Its  chief  stars 

are  :  5,  3  ;  ft  3i  J  «2,  f ,  7>  a11  3f  • 

Microscopium  (The  Microscope)  is  a  small  southern  constella- 
tion whose  brightest  star,  0l,  is  only  4|. 

Equuleus  (The  Little  Horse)  is  a  small  constellation  whose 
brightest  star,  a,  is  only  4. 

Indus  (The  Indian)  is  a  small  southern  constellation  whose 
brightest  stars  are  :  a,  3,  and  ft  3!  ;  but  e  of  mag.  5^  is  distin- 
guished for  its  remarkably  large  proper  motion. 

Piscis  Australis  (The  Southern  Fish)  has  only  one  bright  star, 
a  (Fomalhaut),  \\. 

Cephetis  is  a  large  and  straggling  constellation  which  reaches 
nearly  to  the  North  Pole.  Its  chief  stars  are  :  a  (Alderamin) 
2i  ;  ft  y,  C,  i?,  i,  all  about  3$. 

Grus  (The  Crane)  is  a  southern  constellation  which,  though 
small,  contains  a  considerable  number  of  important  stars. 
These  are  :  a,  2  ;  ft  2|  ;  y,  3  ;  6,  3^. 

Aqtiarius  (The  Water-bearer)  has  for   its  2  principal  stars 
/i  and  a,  both  about  3  ;  8,  <?,  3^  ;  and  e,  f,  3! . 
21 


322        CONSTELLATIONS,    fcA.,    22  H.    2$  M.    TO    OH.    O  M. 

Lacerta  (The  Lizard)  is  a  small  northern  constellation,  of 
which  the  largest  star,  a,  is  only  4  :  but  there  are  1 5  other  stars 
up  to  5i 

Pegasus  (The  Winged  Horse).  The  so-called  "  Square  of 
Pegasus  "  (of  which  a  Andromeda,  sometimes  called  d  Pegasi, 
is  one  member)  is  familiar  to  most  star-gazers.  The  chief  stars 
of  Pegasus  are  :  e,  a  (Markab),  /3  (Scheat),  all  about  2^  ;  y 
(Algenib),  13 >  3  ;  £  3^  ;  and  /*,  0,  3|.  There  are  30  stars  4  to  sJr. 

Toucan  (The  American  Goose).  This  southern  constellation 
only  includes  one  bright  star,  a  2}. 

Octans  (The  Octant)  is  the  constellation  which  includes  the 
South  Pole.  The  brightest  star  is  /u,  3! ;  but  the  nearest  star  to 
the  Pole  is  <r,  $f . 


APPENDIX    I. 

STATISTICS  RESPECTING  THE   PLANETS 
AND  THEIR  SATELLITES. 


ijrs 

X  cs       J3 
<J  O 


c  >>    ~ 
S»oS 

£'S   o 


lO          1-1 

o\     o 


OO 
TJ- 


n 

?o 


VI  —    « 

I     I     I 


bb 


1-1          <N         00 


Ti- 

VO 


vO        QO          CO 
CO        VO          CO         t^ 
rr        O 


^ 

o^^o 

i-i  ro        VO 


cot-^o        ION        IOM         O 
O         O         '<->         «         io        O\        ON        O 


£     S    .S    | 

S      >      H      S 
323 


SOME  STATISTICS  OF  THE  SATELLITES  OF 
THE  PLANETS. 


Name  or 
Number. 

Inclination 
of  Orbit. 

Eccen- 
tricity. 

Mean  Daily 
Motion. 

Sidereal 
Period. 

Mass. 

THE  SATELLITE  OF  THE  EARTH. 

O         1         tt 

o      /      // 

d.    h.    m. 

The  Moon 

5     8  47 

0-0549 

13  10  35 

27     7  43 

0-012552 

THE  SATELLITES  OF  MARS. 

o         / 

0 

d.    h.    m. 

Phobos     . 

27    28 

0-0217 

1128-8 

0     7     39 

? 

Deimos    . 

27   24 

0-0031 

285-1 

i     6     17 

? 

THE  SATELLITES  OF  JUPITER. 

o        / 

o 

d.  h.    m. 

V    .     . 

2    2O 

O'OO5O 

722-6 

o  ii  57 

? 

I    .     . 

2      8 

? 

203-4 

i   18  27 

00000  1 

II    .     . 

I    .38 

? 

107-3 

3  13  13 

O'OOOO2 

Ill    .     . 

i  59 

O'OCOI 

50-3 

7     3  42 

0-00008 

IV    .     . 

i  57 

0-0072 

21-5 

16  16  32 

0-00004 

VI    .     . 

28  56 

0-156 

i*43 

251 

? 

VII    .     . 

31    o 

0-024 

i  '35 

265 

? 

VIII    .     . 

148  52 

0-33 

o'45 

26  months 

? 

THE  SATELLITES  OF  SATURN. 

0           , 

0 

d.  h.   m. 

Mimas 

27  29 

0-019 

381-9 

o  22  77 

0-00000007 

Enceladus 

28     4 

0-004 

2627 

i     8  53 

O'OCOOOO2 

Tethys      . 

28  40 

? 

190-6 

I    21    l8 

O'OOOOOI  I 

Dione 

28    4 

O'OO2 

131-5 

2    17   41 

0-0000018 

Rhea   .     . 

28    22 

0-0009 

79-6 

4  12  25 

0-0000040 

Titan  .     . 

27  39 

O-028 

22'5 

15    22   41 

0-0002127 

Themis    . 

39     6 

0-23 

17.27 

2O   2O   24 

? 

Hyperion. 

27  14 

0-129 

16-9 

21       6    38 

? 

lapetus     . 

18  28 

O-O28 

4'5 

79     7  56 

O'OOOOI 

Phrebe      . 

i/5     5 

0-I65 

0-6 

55°  I0  34 

? 

THE  SATELLITES  OF  URANUS. 

o        / 

0 

d.   h.    m. 

Ariel    .     . 

97     5 

O'O2 

I42-8 

2   12  29 

\Between 

Umbriel  . 

98    2 

O'O  I 

86-8 

4     3  27 

o-oooo  i 

Oberon     . 

98     i 

? 

4i-3 

8  16  56 

and 

Titania     . 

98  17 

•? 

26-7 

13  "     7 

}  0-00005 

THE  SATELLITE  CF  NEPTUNE. 

O            1 

0 

d.  h.    m. 

142  40 

O-OO7 

61-2 

5    21       2 

? 

(From  the  Connaissance  des  Temps,  1912.) 
324 


APPENDIX    II. 


CATALOGUE  OF  CELESTIAL  OBJECTS 
EASY  FOR  SMALL  TELESCOPES. 

THE  following  Catalogue  includes,  with  objects  already  men- 
tioned, others  which  may  be  seen  without  difficulty  in  small 
telescopes ;  though,  to  bring  out  their  specially  attractive 
features,  large  telescopes  may  often  be  necessary. 


PLANETS. 


MERCURY. 

VENUS. 

MARS. 


CERES. 

JUPITER. 

SATURN. 


DOUBLE    STARS,    CLUSTERS,   AND    NEBULA.1 

No  double  star  is  included  unless  bright  enough  to  be  easily 
found  (as  a  single  star)  with  the  naked  eye,  and  unless  the 
two  components  are  at  least  4"  or  5"  apart. 


No. 

Name. 

R.A. 

Dec!. 

Description. 

I 

2 

3 

47  Toucani  . 
31     M     Andro- 
raedae   .     .     . 
r)  Cassiopeia;     . 

h.    m.    s. 

o  19  36 

o  37  19 
o  43     3 

-72   3» 

+  4°  43 
+  57  J7 

Superb  globular  cluster. 

"  The  Great  Nebula." 
Double   star,  mags.   4, 
7±  :  dist.  5". 

Extracted  from   The  Cycle  of  Celestial  Objects  by  Smyth  and   Chambers, 
d  ed.,  price  6s.    An  indispensable  companion  to  every  telescope. 

325 


326 


APPENDIX. 


No. 

Name. 

R.A. 

Decl. 

Description. 

h.    m.     s. 

0           , 

4 

Nubecula  Minor 

o  49     8 

-73  55 

Mass  of  nebula. 

5 

7  Arietis  .     .     . 

I    48      2 

+  18  18 

Double  star,  mags.  4^, 

5  :  dist.  8". 

6 

7  Andromedce  . 

i  57  45 

+  41  51 

Double  star,  mags.  3^, 

5^  :  dist.  10". 

7 

33  y  VIPersei. 

2    12      2 

+  56  41 

Double  cluster  in  fine 

field. 

8 

o  Ceti       .     .     . 

2    14    17 

-  3  25 

Celebrated       variable, 

max.    mag.   2  :    fiery 

red,  invisible  at  min. 

9 

a  Ceti       .     .     . 

2  57    3 

+   3  4i 

Orange  star,  mag.  2^. 

10 

|8  Persei   .     .     . 

3     i  39 

+  40  34 

Variable  star,  max.   2, 

min.  4. 

ii 

77  Tauri    . 

3  4i  32 

+  23  47 

Chief     star      in      the 

"  Pleiades." 

12 

5  Orionis       .     . 

5  26  53 

—    O   22 

Double    star,   mags.    2 

and  7  :  dist.  53" 

J3 

I  M  Tauri     .     . 

5  28  27 

+  21  57 

"The  Crab"  nebula. 

H 

42  M  Orionis 

5  3°  20 

-  5  27 

"The  Great  Nebula  in 

Orion"    surrounding 

the  star  6. 

15 

a-  Orionis      .     . 

5  33  33 

-  2  37 

Multiple  star,  mags.  4, 

8,  and  7:  dist.  12"  and 

42"  :  other  stars. 

16 
17 

30  Doradus  .     . 
35  MGeminorum 

5  39  29 
6     2  40 

-69    9 

+  24    21 

In  the  Nubecula  Major. 
Fine  cluster  of  stars. 

18 

5  Lyncis  .     .     . 

6  18    6 

+  58    28 

Fiery  red  star,  mag.  5^. 

19 

41      M      Canis 

Majoris     .     . 

6  42  39 

-20  37 

Cluster  of  stars. 

20 

fj,  Canis  Majoris 

6  51  32 

-13  55 

Fiery  red  double  star, 

mags.  5^  and  9^  :  dist. 

3"- 

21 

a  Geminorum  . 

7  28  13 

+  32    6 

Double   star,    mags.   3 

and  3^  :  dist.  5". 

22 

7  Argils  .     .     . 

S     6  26 

-47    o 

Double   star,  mags.    2 

and  6  :  dist.  42". 

23 

44  M  Cancri 

8  34  30 

+  20  17 

Loose  cluster,"Prsesepe." 

24 

77  Argus    .     .     . 

10  41   10 

-59    9 

"The  Great  Nebula  in 

Argo,"     surrounding 

the  star  77. 

APPENDIX. 


327 


No. 

Name. 

R.A. 

Decl. 

Description. 

h.    m.    s. 

0            1 

25 

54  Leonis     .     . 

ie  50  12 

+  25  17 

Double  star,  mags.  4^ 

and  7  :  dist.  6". 

26 

a  Crucis  .     .     . 

12   21      O 

-62  33 

Quintuple  star,  mags.  i|, 

2,  and  5:  dist.  5",9o'r. 

27 

y  Crucis  .     .     . 

12   25    36 

-56  33 

Star,  mag.  2,  Companion, 

mag.   5  :  dist.  120". 

28 

7  Virginis     .     . 

12    36    36 

-  o  54 

Binary  star,  both  mag. 

4  :  dist.  6". 

29 

K  Crucis   .     .     . 

12  47  42 

-59  48 

Remarkable  cluster. 

30 

a  Canum  Venat  . 

12    51    2O 

+  38  51 

Double  star,  mags.  2| 

and  6|  :  dist.  20". 

31 

f  Ursae  Majoris 

13  19  54 

+  55  27 

Double  star,  mags.  3  and 

5  :  dist.  14"  :  Alcor, 

mag.  5,  is  distant  I  if  . 

32 

w  Centauri    .     . 

13  20  45 

-46  48 

Large  globular  cluster. 

33 

a  Centauri    .     . 

H  32  47 

-60  26 

Double,  mags.  I  and  2, 

dist.  22". 

34 

TT  Bootis  .     .     . 

14  36    2 

+  16  50 

Double   star,  mags.  3^ 

and  6  :  dist.  6". 

35 

)8  Librae   .     .     . 

15  ii  37 

-  9    o 

Mag.    2|  :    pale   green 

colour. 

36 

5  M  Librae  .     . 

i5  13  27 

+    2    28 

Loose  cluster. 

37 

£  Scorpii  .     .     . 

15  58  52 

-ii     6 

Double  star,  mags.  4  5 

and    7^  :    dist.    7"  ; 

A  also  double. 

38 

j3  Scorpii  .     .     . 

15  59  37 

-19  3i 

Double   star,   mags.    2 

and    5!  :   dist.   13"  ; 

A  also  double. 

39 

v  Scorpii  .     .     . 

16    6  ii 

—  19    12 

Double    star,   mags.    4 

and  7:  dist.  40";  both 

stars  also  double. 

40 

a  Scorpii  .     .     . 

16  23  16 

—  26    12 

Double  star,    mags,    i 

and  7  :  dist.  3"  ;  fiery 

red  star. 

4i 

13  M  Herculis  . 

16  38    6 

+  36  37 

Very    bright    globular 

cluster. 

42 

a  Herculis    .     . 

17  10    5 

+  14  3° 

Double  star,  mags.  3^ 

and  5!  :  dist.  5". 

43 

92  M  Herculis  . 

17  14    4 

+  43  H 

Globular  cluster. 

44 

8  M  Sagittarii   . 

17  57  45 

-24   22 

Bright  irregular  nebula. 

328 


APPENDIX. 


No. 

Name. 

R.A. 

Decl. 

Description. 

h.    m.    s. 

0           , 

45 

17  M  Scuti  So- 

bieskii  .     .     . 

18  14  50 

—  16  14 

"The  Omega  Nebula." 

46 

e  Lyroe 

18  41     i 

+  39  34 

Double  -  double       and 

multiple  star. 

47 

II  M  Antinoi    . 

18  45  45 

-  6  23 

Loose  cluster. 

48 

57  M  Lyrse  .     . 

18  49  50 

+  32  54 

Annular  Nebula. 

49 

Q  Serpentis 

18  51   15 

+  4    5 

Double  star,  mags.  4| 

and  4  :  dist.  21". 

5° 

/3Cygni    .     .     . 

19  26  41 

+  27  45 

Double   Star,   mags.  3 

and  7  :  dist.  34". 

51 

X  Cy8ni    •     •     • 

19  46  44 

+  32  40 

Variable  star,  max.  mag. 

4,  and  red  :  invisible 

at  minimum. 

52 

27  M  Vulpeculoe 

*9  55  M 

+  22    26 

"The       Dumb  -bell" 

Nebula. 

53 

a?  Capricorn!     . 

2O    12    30 

-12    51 

Wide  pair  of  stars,  mags. 

3  and  4  :  dist.  376"  ; 

a  multiple  object. 

54 

/32  Capricorni     . 

20    15    24 

-15    5 

Wide  pair  of  stars,  mags. 

35-  and  7  :  dist.  205". 

55 

7  Delphini    .     . 

2O  42       I 

+  15    46 

Double   star,    mags.    4 

and  6^:  dist.  n". 

56 

15  M  Pegasi      . 

21    28    15 

-   i   16 

Globular  cluster. 

57 

|8  Cephei  .     .     . 

21    27    22 

470    7 

Double   star,   mags.    3 

and  8  :  dist.  13". 

58 

2  M  Aquarii 

21    28    15 

-   i  16 

Fine  globular  cluster. 

59 

/j,  Cephei  .     .     . 

21    40   26 

+  58  19 

Variable  star,  max.  mag. 

4,  min.  6  :  deep  garnet 

in  colour. 

60 

5  Cephei  .     .     . 

22    25    27 

+  57  54 

Variable  star,  max.  mag. 

3^,    min.    45  ;    also 

double,     Companion 

mag.  7  :  dist.  40". 

61 

8  Andromedse  . 

23  13    7 

+  48  27 

Fiery  red  star,  mag.  5. 

62 

30  Piscium  .     . 

23  56  49 

-   6  34 

Fiery  red  star,  mag.  4^. 

INDEX. 


The  titles  of  the  chapters  are  in  small  capitals. 


Achromatism  of  telescopes,  258 
Adams,   J.    C.,   his  researches   as   to 
Neptune,  103  ;    meteor  comets,  188 
Aerolites,  188 
Age  of  the  Moon,  27 
Airy,  Sir  G.  B.,  103 
Algol,  /3  Persei,  212 
Almanacks,  89,  290 
Altazamuth  mounting,  260 
Anagram  on  Venus,  76 
Andromeda  (constellation),  310,  313; 
meteors  of,  174  ;    Great  Nebula  in, 
235 

Annular  eclipses  of  the  Sun,  116 
Annular  nebulae,  227,  232 
Aphelion,  59 
Apogee,  116 
Apparent  movements  of  the  planets 

56 

Appendix  I.,  Statistics  respecting  the 
Planets,  323  ;   Appendix  II.,   Cata- 
logue of  Celestial  Objects,  325 
Aquarius    (constellation),     312,     321  ; 

meteors  in,  174 

Areas,  Equal,  Kepler's  I^aw  of,  60 
Argo  (constellation),  311,  316;    Great 

Nebula  in,  238  ;   Star  TJ  in,  238 
Ascension,  Right,  251,  310 
Asteroids,  109 

Astrca  (Minor  Planet),  108  ;  name  sug 
gested  for  Uranus,  100 

329 


Astronomy,  Different  branches  of,  2 
Atlases,  Celestial,  246 
Aurora  Borealis,  15 

Axial   rotation   of   the   planets,    323  ; 
of  the  Earth,  192 


Baily's  Beads,  122 

Barnard,  E.  E-,  97 

Bayer,  J.,  his  Star  Atlas,  197 

Beer  and  Madler's  Map  of  the  Moon,  29 

Belts  of  Jupiter,  84  ;    of  Saturn,  96  ; 

of  Uranus,  101 
Berthon,  Rev.  E-  I/.,  his  observatory, 

279 

Biela's  Comet,  186 
Binary  stars,  207 

Birds  during  eclipses  of  the  Sun,  119 
Bode,  J.  E-,  his  so-called  I/aw,  107  ; 

suggests  a  name  for  Uranus,  100 
Bond,  G.  P.,  91 
Books  for  use  in  an  observatory,  246, 

325 

"  Bore  "  on  rivers,  52 
Borelly's  Periodical  Comet,  158,  169 
Bouvard,  A.,  102 
Bredechin,    his    classification    of    the 

tails  of  comets,  154 
Brodie,  C.  G.,  182 

Brooks,  W.  R.,  comets  discovered  by, 
145,  158,  169,  17* 


330 


INDEX. 


Brorsen's  Periodical  Comets,  158,  160 
Burnham,  S.  W.,  208 


Calendar,  Reform  of,  285 

Calorific  rays  of  the  Sun,  23  ;    of  the 

Moon,  39 
Cancer     (constellation),      311,      316; 

"  Praesepe  "  in,  228 
Canes    Venatici    (constellation),    311, 

318  ;   spiral  nebula  in,  233 
Cassegrainian  telescope,  257 
Cassini,  J.  D.,  86 
Cassiopeia    (constellation),    310,    313  ; 

temporary  star  in,  218 
Catalogue  of  celestial  objects  for  small 

telescopes,  325 
Cepheus,  312,  321  ;    variable  star  in» 

214 

Ceres  (Minor  Planet),  107 
Cetus  (constellation),  310,  313  ;    vari- 
able star  in,  211 
Chaldaean  Astronomy,  118 
Challis,  Rev.  J.,  103,  150 
Chepstow,  Tides  at,  48 
Cheseaux,  De,  and  the  comet  of  1744, 

152 

Christie,  Sir  W.  H.  M.,  34 
Chromatic  aberration,  258 
Chromosphere  of  the  Sun,  13 
Churchill,  W.  S.,  33 
Circles  for  telescopes,  262 
Circumpolar  stars,  195 
Clapham,  T.  R.,  his  observatory,  280 
Clocks  for  observatories,  263 
Clusters  and  nebulae,  226 
Coggia's  Comet  of  1874,  167 
Coloured  stars,  209 
Colours  Of  stars,  209 
Columbus,   Christopher,   anecdote   of, 

139 
Coma   Berenices    (constellation),    311, 

318  ;  stars  in,  229 
Coma  of  a  comet,  148 
COMETS,  144;  periodical,  156;  re- 


markable, 164  ;    meteors  connected 

with,  187 
Comparative    sizes    of    the    Sun    and 

planets,  63 

Complementary  colours,  209 
Conjunction  of  the  planets,  57  ;    see 

also  64 
CONSTELLATIONS,  THE,  244  ;    lists  of, 

310  ;    how  to  study,  245  ;   see  also 

313  et  seq. 

CONSTELLATIONS,  TABLE  OF  THE,  310 
Corona  in  eclipses  of  the  Sun,  123 
"  Crab  Nebula  "  in  Taurus,  326 
Craters  on  the  Moon,  29 
Cross,  The  Southern,  317 
Cygnus     (constellation),     312,     321  ; 

temporary  star  in,  222  ;  nebulae  in, 

240 

D 

Daniel's  Comet,  170 

Darkness  during  eclipses,  119 

D' Arrest's  Comet,  158 

Dawes,  W.  R.,  12,  91,  208 

Day  as  a  unit  of  time,  287  ;   divisions 

of,  288 
Declination    axis    of    an    equatorial, 

260 
Declination  of  a  heavenly  body,  251, 

310 
Denning,  W.  F.,  69  ;  his  observations 

of  meteors,  175 
Diagonal  eye-piece,  257 
Diameter   of    the    Sun  and    planets, 

323 

Dimensions  of  the  solar  system,  63 
Diurnal  movements  of   the   heavens, 

193 

Di  Vice's  long-period  comet,  160 
Domes  for  observatories,  274 
Donati's  Comet  of  1858,  146 
Dorado      (constellation),      311,      314; 

nebula  in,  237 
Double  stars,  205 
"  Dumb-bell  "  Nebula,  240 


INDEX. 


331 


Earth,  55 

Earth-shine,  36 

Eccentricity  of  orbits,  60 

ECLIPSES,  113 

Eclipse  expeditions,  129 

Eclipses,  General  outlines  of,  113; 
future,  127 

Eclipses  of  Jupiter's  satellites,  143 

Eclipses  of  the  Sun,  114,  121  ;  ob- 
served at  sea,  135 

Eclipses  of  the  Moon,  116 

Ecliptic,  Obliquity  of,  58 

Ellipse,  Properties  of,  60 ;  how  to 
draw,  6 1 

Elliptic  nebulae,  227,  232 

Elongation  of  Mercury,  68 

Encke,  J.  F.,  104 

Encke's  Comet,  158 

Equation  of  time,  44,  298 

Equatorial  instrument,  260 

Eros  (Minor  Planet),  no 

"  Establishment  of  the  Port,"  45 

Eye-pieces,  258 


Faculae  on  the  Sun,  24 
Faye's  Periodical  Comet,  158 
Finlay's  Periodical  Comet,  158 
Fire-balls,  178,  180 
Flames,  Red,  on  the  Sun,  122 
Flamsteed,  Rev.  J.,  198 
Foundations  for  an  observatory,  268 
Fraiinhofer,  J.,  303 
Full  Moon,  27,  36 


Galaxy,  242 

Galilean  telescope,  259 

Galle,  J.  G.,  91,  104 

Gemini      (constellation),      311,      315  ; 

meteors  in,  175,  177 
Georgium  Sidus,  100 
Giacobini's  Comet,  169 


Gladstone,  W.  E.,  253 
Globular  clusters,  230 
Granulations  on  the  Sun's  surface,  7 
Gravitation,  Theory  of,  59,  206 
Greenwich  Observatory,  201 
Gregorian  calendar,  286 
Gregorian  telescope,  257 
Grimthorpe,  I^ord,  2 
GROUPS  OF  STARS  AND  NEBULA,  226 


II 


Hale,  G.  E-,  20 

Halley,  E.,  160 

Halley's  Comet,  161,  170 

Harvard  Photometry  cited,  196 

Harvest  Moon,  32 

Heat-rays  of  the  Sun,  23 

Helium,  306,  308 

Hencke,  K.  C.,  his  search  for  minor 

planets,  108 
Hercules     (constellation),     312,     320; 

cluster  in,  230 
Herschelian  telescope,  257 
Herschel,  Sir  J.  F.  W.,  62,  199 
Herschel,  Sir  W.,  98,  109,  205 
High- water,  42,  43 
Hipparchus,  285 
Holmes's  Periodical  Comet,  158 
Homer  cited,  253 
"  Horse-shoe  "  Nebula,  239 
Hour-circle,  262 
Hours,  283 

Huggins,  Sir  W.,  7,  232,  233,  308 
Hunter's  Moon,  33 
Hyades,  The,  in  Taurus,  227 
Hygre  (tidal  phenomenon),  52 
Hyperbola,  157 
Hyperbolic  comets,  157 


Inclination  of  the  Ecliptic,  59,  117; 

of  a  planet's  orbit,  59 
Inferior  Planets,  56 


332 


INDEX. 


Intra-Mercurial  planets,  66 

Iron,  Meteoric,  189 

Isle  of  Wight,  Tides  around,  51 


Johnson,  Rev.  S.  J.,  127 
Johnston,  A.  K.,  50 
Jupiter,  84 

K 

Kepler's  I,aws,  59 

Klein,  H.  J.,  his  Atlas,  246 

Kullmer's  Star-finder,  247 


199 

"  gagging  "  of  the  tides,  46 

I^alande,  J.  J.,  100 

I^angley,  S.  P.,  7,  12 

I/a  Place,  100 

Ivassell,  W.,  1 01 

I,aVerrier,  U.  J.  J.,  103 

I<eo  (constellation),  311,  317  ;  meteors 
in, 174, 187 

Leonid  meteors,  187 

I^ewis,  Sir  G.  C.,  199 

I<ibra  (constellation),  312,  318  ;  cluster 
in,  230 

I,ibrations  of  the  Moon,  31 

Ivight-pressure,  156 

Ivight,  transmission  of ,  90 

lyow  water,  43 

Lumtire  Cendree  on  the  Moon,  36 

3+yra  (constellation),  312,  32O  ;  an- 
nular nebula  in,  232  ;  meteors  in, 
174  J  multiple  star  e  in,  328 

M 

*Madler,  J.  H.,  29 
Magellanic  Clouds,  241 
Magnetism,  terrestrial  and  solar  spots 
15 


Magnitude  of  stars,  196,  200  ;  list  of 
stars  of  the  first  magnitude,  248 

Magnitude  of  the  solar  system,  popular 
illustration  of,  62 

Maps,  Astronomical,  245 

Mars,  77  ;  phases  of,  78  ;  markings 
on,  8 1  ;  satellites  of ,  83  ;  see  also  58 

Maunder,  B.  W.,  17,  299 

Mean  distance  of  a  planet,  323 

Medal  struck  by  monks,  1680,  153  ; 
the  Warner  Prize,  164 

Mediterranean  Sea,  tides  in,  48 

Mercury,  68  ;  phases  of,  57  ;  transits 
of,  142  ;  see  also,  56 

Messier,  his  catalogue  of  nebulae,  229 

Meteoric  stones,  189 

Meteors,  Telescopic,  173 

Milky  Way,  242 

Minor  planets,  106 

MiraCeti,  212,  326 

Months,  283,  285 

Montigny,  C.,  his  researches  on  twink- 
ling, 203 

MOON,  THE,  26  ;  phases  of,  27  ;  and 
the  weather,  34  ;  genuine  weather 
influences,  37  ;  as  a  measurer  of  time, 
285,  287  ;  mountains  on,  28 

Moonlight,  Brightness  of,  34 

Moore,  Admiral,  54 

Morehouse's  Comet,  170 

Motions  of  the  planets,  55,  57,  58 

Mountains  suspected  on  Mercury,  69  ; 
on  Venus,  74 

Multiple  stars,  205 


N 


Naked-eye,  number  of  stars  visible 
to,  201 

Nasmyth,  J.,  "his  willow-leaves"  on 
the  Sun,  7 

Nautical  Almanack,  89,  100,  294 

Neap  Tides,  45 

Nebulae,  231  ;  varieties  of,  227  ;  dis- 
tribution of,  241 


INDEX:. 


333 


Nebulous  stars,  227 

Needle,    Magnetic,    variation    in    the 

declination  of,  16 
Neptune,  101 
New  stars,  218 
Newton,  Sir  I.,  160,  302 
Newtonian  telescope,  257 
Node,  Ascending,  58  ;   Descending,  58 
November  meteors  (I^onids),  186,  187 
Nubecula  Major,  241 
Nubecula  Minor,  241 
Nucleus  of  a  Sun-spot,  12  ;  of  a  comet, 

148 


Object-glass,  258 
Observations  of  eclipses,  129 
Observatory,    264  ;     construction    of, 

264 

Occultations,  143 
"  Omega,  nebula, "in  ClypeusSobieskii, 

239 

Opera-glass,  259 

Ophiucus,  312,  320  ;   new  star  in,  220 
Oppolzer,    T.    von,    his    catalogue    of 

eclipses  cited,  128 
Opposition,  Planets  in,  57 
Optical  double  stars,  205 
Orbits  of  planets,  58  ;   of  comets,  156  ; 

of  double  stars,  206  ;  of  meteors,  186 
Orion  (constellation),  311,  315  ;    Great 

Nebula  in,  236  ;  meteors  in,  174 


Pacific  Ocean,  Tides  in,  49 

Pallas  (Minor  Planet),  107 

Parabola,  157 

Parallax,  206 

Pegasus  (constellation),  312,  322  ;    the 

"  square  "  of,  322 
Penumbra  of  a  Sun-spot,  12 
Perigee,  116 
Perihelion,  59 

Periodic  comets,  156,  158,  if>o 
Periodicity     of     Sun-spots,     14  ;      of 

shoo  ting  stars,  173 


Periods  of  the  planets,  323  ;  of  comets, 
158,  160 

Perseus  (constellation),  310,  314  ; 
cluster  in,  326;  new  star  in,  219, 
223  ;  meteors  in,  173 

Perturbations  of  Uranus  by  Neptune, 
102 

Phases  of  Inferior  Planets,  57  ;  of  the 
Moon,  27  ;  of  Mars,  78  ;  of  Jupiter, 
57  ;  of  Saturn's  Rings,  92 

Photometer,  196 

Photometry  of  the  stars,  196 

Photosphere  of  the  Sun,  13 

Pickering,  E.  C.,  224 

Pickering,  W.  H.,  82  ;  his  classifica- 
tion of  the  tails  of  comets,  155 

Pillar -and-claw  stand,  260 

PLANETS  GENERALLY,  THE,  55 

PLANETS,  THE  FAMILIAR,  67 

PLANETS,  THE  I^ESS  KNOWN,  98 

Planetary  nebulae,  227 

Planetoids.     See  Minor  Planets 

Planispheres,  245 

Plans  and  specifications  of  an  observa- 
tory, 264 

Pleiades,  227 

Pole-Star  (a  Ursse  Minoris),  195,  252, 

254 

Pons's  Periodical  Comet,  160 
Prsesepein  Cancer,  228 
Prime  Meridian,  289 
"Priming  and  lagging"  of  the  tides, 

46 

Principia,  Newton's,  161 
Proctor,  R.  A.,  5 
Prominences,  Solar,  122 
Ptolomy,  C.,  his  system,  66 


Q 

Quadrans      Muralis      (constellation), 

meteors  in,  174 
Quadrature  of  the  Moon,  43  ;    planets 

in,  58 

Quadruple  stars,  205 
Quarters  of  the  Moon,  27 


334 


INDEX. 


Radiant-points  of  meteors,  174 

Radius-vector  of  a  planet,  60 

Rainfall  and  Sun-spots,  17 

Range  of  the  tides,  45 

"  Red  Flames  "  in  eclipses  of  the  Sunj 

122 

Red  spot  on  Jupiter,  85 
Reflecting  telescopes,  256 
Refracting  telescopes,  256 
"  Rice-grains  "  on  the  Sun,  6 
Right  Ascension,  251 
Rings  of  Saturn,  91 
Roberts,  I.,  233 

Romer,  Observations  of,  on  I/ight,  90 
Rordame's  Comet,  168 
Rosse,  Third  E)arl  of,  232,  233 
Rotation    of    the    Sun,    10 ;     of    the 
planets,  232 


Sagittarius  (constellation),   312,   320; 

nebula  in,  238 
Saros,  118 
Satellites  of  Mars,  83  ;  of  Jupiter,  87  ; 

of  Saturn,  96  ;   of  Uranus,  101  ;    of 

Neptune,  106 
Saturn,  91  ;  belts  of,  96  ;  satellites  of, 

96 

Schiaparelli,  70 
Schmidt,  J.F.J.,  222 
SchrSter,  J.  J.,  73 

Schwabe,    H.,    observations    of    Sun- 
spots,  14 
Scorpio     (constellation),     312,     319  ; 

variable  cluster  in,  231 
Scutum  Sobieskii  (constellation),  312, 

328  ;   nebula  in,  239 
Seabroke,  G.  M.,  double-star  observer, 

208 

Seas,  I^unar,  29 
Secchi,  A.,  208,  301  ;    his  Star-types, 

204,  306 
Semi-axis-major  of    a  planet's  orbit, 

62 


Shadow-bands  in  eclipses  of  the  Sun, 
124 

Shadow  cast  by  Venus,  74  ;  of  the  Moon 
during  eclipses  of  the  Sun,  123 

SHOOTING-STARS,  172 

Signs  of  the  Zodiac,  284 

Silvered-glass  reflectors,  257 

Site  for  an  observatory,  265,  266 

Smyth,  Admiral,  W.  H.,  325 

Snow  suspected  on  Mars,  80 

SPECTROSCOPE,     THE,     ASTRONOMIC- 
ALLY, 301 

Spectrum  analysis,  301 

Spherical  aberration,  258 

Sporadic  meteors,  173 

Spots  on  the  Sun,  9  ;   on  Jupiter,  84  ', 
on  Saturn,  96 

Spring  Tides,  45 

Standard  time,  290 

Stands  for  telescopes,  260 

STARS,  THE,  191 
Star -finder,  Kullmer's,  247 
Stars,   Magnitudes   of,    200 ;     double, 
205  ;    binary,  206  ;    multiple,    205  ; 
variable,     211;      temporary,     218; 
coloured,  209 
Stewart,  B.,  19 
Stone,  U.  J.,  18,  137 
Struve,  F.  G.  W.,  208 
Styles  old  and  new,  286 
SUN,  THE,  5 

Sun,  Spots  on,  9  ;   periodicity  of,  14 
Superior  Planets,  56 
Swift,  Dean,  83 

Swift's  Periodical  Comets,  158,  168 
Symbols  of  the  Major  Planets,  323 


Tables  of  the  Planets  and  Satellites, 

323 

Tails  of  comets,  153 
Taurus      (constellation),      311,      314  ; 

"Crab  Nebula"  in,  326;    meteors 

in,  175  ;  the  Pleiades  and  Hyadesin, 

227 


INDEX. 


335 


TELESCOPES,  256 

Telescopes,  various  kinds  of,  256  ; 
hints  as  to  the  purchase  of,  259 ; 
stands  for,  260  ;  equatorial  mount- 
ing of,  260 

Telescopic  comets,  147 

Telescopic  meteors,  173 

Tempel,  W.,  228 

Tempel's  Periodical  Comets,  158 

Temporary  stars,  218 

Terminator  of  the  Moon,  30 

Tidal-day,  Definition  of ,  44 

TIDES,  THE,  41 

TIME  AND  ITS  MEASUREMENT,  283 

Time,  Equation  of,  298 

Time  gun,  23 

Total  eclipses  of  the  Sun,  119,  121  ; 
of  the  Moon,  138 

Toucan  (constellation),  312,  322; 
cluster  in,  229,  239,  325 

Trans-Neptunian  planet  (the  sup- 
posed), 66 

Transit  Circle,  298 

Transit  Instrument,  294 

Transit  of  planets,  141  ;  of  Mercury, 
142  ;  of  Venus,  142  ;  of  Jupiter's 
satellites,  143 

Trapezium  of  Orion,  236 

Triple  stars,  205 

Tuttle's  Periodical  Comet,  158 

Twinkling,  202 

Tycho  Brahe,  218  ;   his  system,  66 


U 


Uranus,  98  ;    general  account  of,  y8  ; 

satellites  of ,  101 
Ursa  Major  (constellation),  311,  317; 

planetary  nebula  in,  235 


Variable  nebula,  231 

Variable  stars,  211 

Velocity  of  light,  90  ;  of  the  tidal  wave, 
5i 

Venus,  73  ;  transits  of,  142  ;  sus- 
pected influence  on  Sun-spots,  19  ; 
phases  of,  57 

Vesta  (Minor  Planet),  107 

Vorticose  movements  on  the  Sun,  20 

Vulpecula  (constellation),  312,  321; 
"  Dumb-bell  Nebula  "  in,  240 


W 

Weather   influences   imputed    to    the 

Moon,  34 

Webb,  Rev.  T.  W.,  181 
Week,  Days  of,  283,  286 
Westphal's  Periodical  Comet,  160 
"  Whirlpool"  or  "Spiral"  nebulae,  22 
"  Willow  leaves  "  on  the  Sun,  7 
Wilson  (Professor   at   Glasgow),    19  ; 

his  theory  of  Sun-spots,  19 
Winnecke's  Periodical  Comet,  158 
Wolf,  Dr.,  his  Periodical  Comet,  158 
Wolf,  R.,  his  observations  on  the  Sun, 

17 
Wollaston,  F.,  his  observations  on  the 

Sun, 303 


Year,  various  kinds  of,  284  ;  length  of 

284 


Zodiac,  motion  of   the  Sun   through, 

285 
Zone  of  Sun-spots,  14 


PRINTED  BY 

HAZELL,  WATSON  'AND  VINEY,  LD., 
LONDON  AND  AYLESBURY. 


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2  g 


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THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


